resync docs, dump_csv: support from the Perl version

I somehow forgot about the existence of the perror(3) function :x

4 files changed, 222 insertions, 143 deletions

diff --git a/Documentation/mwrap.pod b/Documentation/mwrap.pod
index 6832430..a31bc1f 100644
--- a/Documentation/mwrap.pod
+++ b/Documentation/mwrap.pod
@@ -7,8 +7,8 @@ mwrap - run any command under mwrap
   # to trace a long-running program and access it via $DIR/$PID.sock:
   MWRAP=socket_dir:$DIR mwrap COMMAND
 
-  # to trace a short-lived command and dump its output to a log:
-  MWRAP=dump_path:$FILENAME mwrap COMMAND
+  # to trace a short-lived command and dump its output to a CSV:
+  MWRAP=dump_csv:$FILENAME mwrap COMMAND
 
 =head1 DESCRIPTION
 
@@ -46,13 +46,28 @@ This may be changed via POST request (see below).
 
 Default: 0
 
+=item dump_csv:$FILENAME
+
+Dump CSV to the given filename.
+
+This output matches the HTTP server output and includes column headers,
+but is subject to change in future releases.
+
+C<dump_csv> without the C<:> may also be used in conjunction with
+C<dump_fd>, such as C<MWRAP=dump_fd:2,dump_csv>.
+
+As of mwrap 3.0,
+C<$FILENAME> may contain C<%p> where C<%p> is a placeholder for
+the PID being dumped.  No other use of C<%> is accepted, and
+multiple C<%> means all C<%> (including C<%p>) are handled as-is.
+
 =item dump_path:$FILENAME
 
 Dumps the output at exit to a given filename:
 
         total_bytes        call_count        location
 
-In the future, dumping to a self-describing CSV will be supported.
+Expands C<%p> to the PID in C<$FILENAME> as described for C<dump_csv>
 
 =item dump_fd:$DESCRIPTOR
 
diff --git a/README b/README
index 761f87e..f969c14 100644
--- a/README
+++ b/README
@@ -16,20 +16,24 @@ numeric caller addresses for allocations made without GVL so you
 can get an idea of how much memory usage certain extensions and
 native libraries use.
 
+As of 3.0, it also gives configurable C backtraces of all
+dynamically-linked malloc callsites for any program where backtrace(3)
+works, including programs not linked to Ruby.
+
 It requires the concurrent lock-free hash table from the
 Userspace RCU project: https://liburcu.org/
 
 It does not require recompiling or rebuilding Ruby, but only
 supports Ruby 2.7.0 or later on a few platforms:
 
-* GNU/Linux (only tested --without-jemalloc, mwrap 3.x provides its own)
+* GNU/Linux (only tested --without-jemalloc, mwrap 3.x provides its own malloc)
 
 It may work on FreeBSD, NetBSD, OpenBSD and DragonFly BSD if given
 appropriate build options.
 
 == Install
 
-        # Debian-based systems: apt-get liburcu-dev
+        # Debian-based systems: apt-get install liburcu-dev
 
         # Install mwrap via RubyGems.org
         gem install mwrap
@@ -37,13 +41,21 @@ appropriate build options.
 == Usage
 
 mwrap works as an LD_PRELOAD and supplies a mwrap RubyGem executable to
-improve ease-of-use.  You can set dump_path: in the MWRAP environment
-variable to append the results to a log file:
+improve ease-of-use.  You can set `dump_csv:' in the MWRAP environment
+variable to append the results to a CSV file:
+
+        MWRAP=dump_csv:/path/to/log mwrap RUBY_COMMAND
+
+(`dump_csv:' is new in mwrap 3.x, `dump_file:' from earlier versions is
+still supported).
 
-        MWRAP=dump_path:/path/to/log mwrap RUBY_COMMAND
+For long running processes, you can see the AF_UNIX HTTP interface:
 
-        # And to display the locations with the most allocations:
-        sort -k1,1rn </path/to/log | $PAGER
+        MWRAP=socket_dir:/some/dir mwrap COMMAND
+
+And connect via `curl --unix-socket /some/dir/$PID.sock' or
+`mwrap-rproxy(1p)<https://80x24.org/mwrap-perl.git/tree/script/mwrap-rproxy#n44>
+for more info.
 
 You may also `require "mwrap"' in your Ruby code and use
 Mwrap.dump, Mwrap.reset, Mwrap.each, etc.
@@ -53,7 +65,10 @@ effect in tracking malloc use.  However, it is safe to keep
 "require 'mwrap'" in performance-critical deployments,
 as overhead is only incurred when used as an LD_PRELOAD.
 
-The output of the mwrap dump is a text file with 3 columns:
+The output of `dump_csv:' is has self-describing columns and is
+subject to change.  SQLite 3.32+ can load it with: `.import --csv'.
+
+The output of the `dump_file:' output is a text file with 3 columns:
 
         total_bytes        call_count        location
 
diff --git a/ext/mwrap/httpd.h b/ext/mwrap/httpd.h
index ef4d83c..8a105aa 100644
--- a/ext/mwrap/httpd.h
+++ b/ext/mwrap/httpd.h
@@ -221,7 +221,7 @@ static FILE *fbuf_init(struct mw_fbuf *fb)
 {
         fb->ptr = NULL;
         fb->fp = open_memstream(&fb->ptr, &fb->len);
-        if (!fb->fp) fprintf(stderr, "open_memstream: %m\n");
+        if (!fb->fp) perror("open_memstream");
         return fb->fp;
 }
 
@@ -237,7 +237,7 @@ static int fbuf_close(struct mw_fbuf *fb)
 {
         int e = ferror(fb->fp) | fclose(fb->fp);
         fb->fp = NULL;
-        if (e) fprintf(stderr, "ferror|fclose: %m\n");
+        if (e) perror("ferror|fclose");
         return e;
 }
 
@@ -279,7 +279,7 @@ static enum mw_qev h1_200(struct mw_h1 *h1, struct mw_fbuf *fb, const char *ct)
          */
         off_t clen = ftello(fb->fp);
         if (clen < 0) {
-                fprintf(stderr, "ftello: %m\n");
+                perror("ftello");
                 fbuf_close(fb);
                 return h1_close(h1);
         }
@@ -468,7 +468,7 @@ static off_t write_loc_name(FILE *fp, const struct src_loc *l)
         off_t beg = ftello(fp);
 
         if (beg < 0) {
-                fprintf(stderr, "ftello: %m\n");
+                perror("ftello");
                 return beg;
         }
         if (l->f) {
@@ -498,15 +498,17 @@ static off_t write_loc_name(FILE *fp, const struct src_loc *l)
         }
         off_t end = ftello(fp);
         if (end < 0) {
-                fprintf(stderr, "ftello: %m\n");
+                perror("ftello");
                 return end;
         }
         return end - beg;
 }
 
-static struct h1_src_loc *accumulate(unsigned long min, size_t *hslc, FILE *lp)
+static struct h1_src_loc *
+accumulate(struct mw_fbuf *lb, unsigned long min, size_t *hslc)
 {
         struct mw_fbuf fb;
+        if (!fbuf_init(lb)) return NULL;
         if (!fbuf_init(&fb)) return NULL;
         rcu_read_lock();
         struct cds_lfht *t = CMM_LOAD_SHARED(totals);
@@ -528,18 +530,23 @@ static struct h1_src_loc *accumulate(unsigned long min, size_t *hslc, FILE *lp)
                         HUGE_VAL;
                 hsl.max_life = uatomic_read(&l->max_lifespan);
                 hsl.sl = l;
-                hsl.lname_len = write_loc_name(lp, l);
+                hsl.lname_len = write_loc_name(lb->fp, l);
                 fwrite(&hsl, sizeof(hsl), 1, fb.fp);
         }
         rcu_read_unlock();
 
-        struct h1_src_loc *hslv;
-        if (fbuf_close(&fb)) {
-                hslv = NULL;
-        } else {
-                *hslc = fb.len / sizeof(*hslv);
-                mwrap_assert((fb.len % sizeof(*hslv)) == 0);
-                hslv = (struct h1_src_loc *)fb.ptr;
+        if (fbuf_close(&fb) || fbuf_close(lb))
+                return NULL;
+
+        struct h1_src_loc *hslv = (struct h1_src_loc *)fb.ptr;
+        *hslc = fb.len / sizeof(*hslv);
+        mwrap_assert((fb.len % sizeof(*hslv)) == 0);
+        char *n = lb->ptr;
+        for (size_t i = 0; i < *hslc; ++i) {
+                hslv[i].loc_name = n;
+                n += hslv[i].lname_len;
+                if (hslv[i].lname_len < 0)
+                        return NULL;
         }
         return hslv;
 }
@@ -609,124 +616,128 @@ static enum mw_qev each_at(struct mw_h1 *h1, struct mw_h1req *h1r)
         return h1_200(h1, &html, TYPE_HTML);
 }
 
-/* /$PID/each/$MIN endpoint */
-static enum mw_qev each_gt(struct mw_h1 *h1, struct mw_h1req *h1r,
-                                unsigned long min, bool csv)
-{
-        static const char default_sort[] = "bytes";
-        const char *sort;
-        size_t sort_len = 0;
+typedef int (*cmp_fn)(const void *, const void *);
 
-        if (!csv) {
-                sort = default_sort;
-                sort_len = sizeof(default_sort) - 1;
+static cmp_fn write_csv_header(FILE *fp, const char *sort, size_t sort_len)
+{
+        cmp_fn cmp = NULL;
+        for (size_t i = 0; i < CAA_ARRAY_SIZE(fields); i++) {
+                const char *fn = fields[i].fname;
+                if (i)
+                        fputc(',', fp);
+                fputs(fn, fp);
+                if (fields[i].flen == sort_len && !memcmp(fn, sort, sort_len))
+                        cmp = fields[i].cmp;
         }
+        fputc('\n', fp);
+        return cmp;
+}
 
-        if (h1r->qstr && h1r->qlen > 5 && !memcmp(h1r->qstr, "sort=", 5)) {
-                sort = h1r->qstr + 5;
-                sort_len = h1r->qlen - 5;
+static void write_csv_data(FILE *fp, struct h1_src_loc *hslv, size_t hslc)
+{
+        for (size_t i = 0; i < hslc; i++) {
+                struct h1_src_loc *hsl = &hslv[i];
+
+                fprintf(fp, "%zu,%zu,%zu,%zu,%0.3f,%zu,",
+                        hsl->bytes, hsl->allocations, hsl->frees,
+                        hsl->live, hsl->mean_life, hsl->max_life);
+                write_q_csv(fp, hsl->loc_name, hsl->lname_len);
+                fputc('\n', fp);
         }
+}
 
-        size_t hslc;
+static void *write_csv(FILE *fp, size_t min, const char *sort, size_t sort_len)
+{
         AUTO_CLOFREE struct mw_fbuf lb;
-        if (!fbuf_init(&lb)) return h1_close(h1);
-        AUTO_FREE struct h1_src_loc *hslv = accumulate(min, &hslc, lb.fp);
-        if (!hslv)
-                return h1_close(h1);
+        size_t hslc;
+        AUTO_FREE struct h1_src_loc *hslv = accumulate(&lb, min, &hslc);
+        if (!hslv) return NULL;
 
-        if (fbuf_close(&lb))
-                return h1_close(h1);
+        cmp_fn cmp = write_csv_header(fp, sort, sort_len);
+        if (cmp)
+                qsort(hslv, hslc, sizeof(*hslv), cmp);
+        write_csv_data(fp, hslv, hslc);
+        return fp;
+}
 
-        char *n = lb.ptr;
-        for (size_t i = 0; i < hslc; ++i) {
-                hslv[i].loc_name = n;
-                n += hslv[i].lname_len;
-                if (hslv[i].lname_len < 0)
-                        return h1_close(h1);
+/* /$PID/each/$MIN endpoint */
+static enum mw_qev each_gt(struct mw_h1 *h1, struct mw_h1req *h1r,
+                                size_t min, bool csv)
+{
+        static const char default_sort[] = "bytes";
+        const char *sort = csv ? NULL : default_sort;
+        size_t sort_len = csv ? 0 : (sizeof(default_sort) - 1);
+
+        if (h1r->qstr && h1r->qlen > 5 && !memcmp(h1r->qstr, "sort=", 5)) {
+                sort = h1r->qstr + 5;
+                sort_len = h1r->qlen - 5;
         }
 
         struct mw_fbuf bdy;
         FILE *fp = wbuf_init(&bdy);
         if (!fp) return h1_close(h1);
-
-        if (!csv) {
-                unsigned depth = (unsigned)CMM_LOAD_SHARED(bt_req_depth);
-                fprintf(fp, "<html><head><title>mwrap each &gt;%lu"
-                        "</title></head><body><p>mwrap each &gt;%lu "
-                        "(change `%lu' in URL to adjust filtering) - "
-                        "MWRAP=bt:%u <a href=\"%lu.csv\">.csv</a>",
-                        min, min, min, depth, min);
-                show_stats(fp);
-                /* need borders to distinguish multi-level traces */
-                if (depth)
-                        FPUTS("<table\nborder=1><tr>", fp);
-                else /* save screen space if only tracing one line */
-                        FPUTS("<table><tr>", fp);
+        if (csv) {
+                if (write_csv(fp, min, sort, sort_len))
+                        return h1_200(h1, &bdy, TYPE_CSV);
+                return h1_close(h1);
         }
 
-        int (*cmp)(const void *, const void *) = NULL;
-        if (csv) {
-                for (size_t i = 0; i < CAA_ARRAY_SIZE(fields); i++) {
-                        const char *fn = fields[i].fname;
-                        if (i)
-                                fputc(',', fp);
-                        fputs(fn, fp);
-                        if (fields[i].flen == sort_len &&
-                                        !memcmp(fn, sort, sort_len))
-                                cmp = fields[i].cmp;
-                }
-                fputc('\n', fp);
-        } else {
-                for (size_t i = 0; i < CAA_ARRAY_SIZE(fields); i++) {
-                        const char *fn = fields[i].fname;
-                        FPUTS("<th>", fp);
-                        if (fields[i].flen == sort_len &&
-                                        !memcmp(fn, sort, sort_len)) {
-                                cmp = fields[i].cmp;
-                                fprintf(fp, "<b>%s</b>", fields[i].fname);
-                        } else {
-                                fprintf(fp, "<a\nhref=\"./%lu?sort=%s\">%s</a>",
-                                        min, fn, fn);
-                        }
-                        FPUTS("</th>", fp);
+        size_t hslc;
+        AUTO_CLOFREE struct mw_fbuf lb;
+        AUTO_FREE struct h1_src_loc *hslv = accumulate(&lb, min, &hslc);
+        if (!hslv)
+                return h1_close(h1);
+
+        unsigned depth = (unsigned)CMM_LOAD_SHARED(bt_req_depth);
+        fprintf(fp, "<html><head><title>mwrap each &gt;%lu"
+                "</title></head><body><p>mwrap each &gt;%lu "
+                "(change `%lu' in URL to adjust filtering) - "
+                "MWRAP=bt:%u <a href=\"%lu.csv\">.csv</a>",
+                min, min, min, depth, min);
+        show_stats(fp);
+        /* need borders to distinguish multi-level traces */
+        if (depth)
+                FPUTS("<table\nborder=1><tr>", fp);
+        else /* save screen space if only tracing one line */
+                FPUTS("<table><tr>", fp);
+        cmp_fn cmp = NULL;
+        for (size_t i = 0; i < CAA_ARRAY_SIZE(fields); i++) {
+                const char *fn = fields[i].fname;
+                FPUTS("<th>", fp);
+                if (fields[i].flen == sort_len &&
+                                !memcmp(fn, sort, sort_len)) {
+                        cmp = fields[i].cmp;
+                        fprintf(fp, "<b>%s</b>", fields[i].fname);
+                } else {
+                        fprintf(fp, "<a\nhref=\"./%lu?sort=%s\">%s</a>",
+                                min, fn, fn);
                 }
+                FPUTS("</th>", fp);
         }
-        if (!csv)
-                FPUTS("</tr>", fp);
+        FPUTS("</tr>", fp);
         if (cmp)
                 qsort(hslv, hslc, sizeof(*hslv), cmp);
-        else if (!csv)
+        else
                 FPUTS("<tr><td>sort= not understood</td></tr>", fp);
-        if (csv) {
-                for (size_t i = 0; i < hslc; i++) {
-                        struct h1_src_loc *hsl = &hslv[i];
 
-                        fprintf(fp, "%zu,%zu,%zu,%zu,%0.3f,%zu,",
-                                hsl->bytes, hsl->allocations, hsl->frees,
-                                hsl->live, hsl->mean_life, hsl->max_life);
-                        write_q_csv(fp, hsl->loc_name, hsl->lname_len);
-                        fputc('\n', fp);
-                }
-        } else {
-                for (size_t i = 0; i < hslc; i++) {
-                        struct h1_src_loc *hsl = &hslv[i];
+        for (size_t i = 0; i < hslc; i++) {
+                struct h1_src_loc *hsl = &hslv[i];
 
-                        fprintf(fp, "<tr><td>%zu</td><td>%zu</td><td>%zu</td>"
-                                "<td>%zu</td><td>%0.3f</td><td>%zu</td>",
-                                hsl->bytes, hsl->allocations, hsl->frees,
-                                hsl->live, hsl->mean_life, hsl->max_life);
-                        FPUTS("<td><a\nhref=\"../at/", fp);
+                fprintf(fp, "<tr><td>%zu</td><td>%zu</td><td>%zu</td>"
+                        "<td>%zu</td><td>%0.3f</td><td>%zu</td>",
+                        hsl->bytes, hsl->allocations, hsl->frees,
+                        hsl->live, hsl->mean_life, hsl->max_life);
+                FPUTS("<td><a\nhref=\"../at/", fp);
 
-                        write_b64_url(fp, src_loc_hash_tip(hsl->sl),
-                                        src_loc_hash_len(hsl->sl));
+                write_b64_url(fp, src_loc_hash_tip(hsl->sl),
+                                src_loc_hash_len(hsl->sl));
 
-                        FPUTS("\">", fp);
-                        write_html(fp, hsl->loc_name, hsl->lname_len);
-                        FPUTS("</a></td></tr>", fp);
-                }
-                FPUTS("</table></body></html>", fp);
+                FPUTS("\">", fp);
+                write_html(fp, hsl->loc_name, hsl->lname_len);
+                FPUTS("</a></td></tr>", fp);
         }
-        return h1_200(h1, &bdy, csv ? TYPE_CSV : TYPE_HTML);
+        FPUTS("</table></body></html>", fp);
+        return h1_200(h1, &bdy, TYPE_HTML);
 }
 
 /* /$PID/ root endpoint */
@@ -781,7 +792,7 @@ static enum mw_qev h1_dispatch(struct mw_h1 *h1, struct mw_h1req *h1r)
                 if ((c = PATH_SKIP(h1r, "/each/"))) {
                         errno = 0;
                         char *e;
-                        unsigned long min = strtoul(c, &e, 10);
+                        size_t min = (size_t)strtoul(c, &e, 10);
                         if (!errno) {
                                 if (*e == ' ' || *e == '?')
                                         return each_gt(h1, h1r, min, false);
@@ -857,7 +868,7 @@ static enum mw_qev h1_drain_input(struct mw_h1 *h1, struct mw_h1req *h1r,
                                 return h1_close(h1);
                         default: /* ENOMEM, ENOBUFS, ... */
                                 assert(errno != EBADF);
-                                fprintf(stderr, "read: %m\n");
+                                perror("read");
                                 return h1_close(h1);
                         }
                 }
@@ -990,7 +1001,7 @@ static enum mw_qev h1_event_step(struct mw_h1 *h1, struct mw_h1d *h1d)
         if (!h1r) {
                 h1r = h1d->shared_h1r = malloc(sizeof(*h1r));
                 if (!h1r) {
-                        fprintf(stderr, "h1r malloc: %m\n");
+                        perror("h1r malloc");
                         return h1_close(h1);
                 }
         }
@@ -1034,7 +1045,7 @@ static enum mw_qev h1_event_step(struct mw_h1 *h1, struct mw_h1d *h1d)
                                 return h1_close(h1);
                         default: /* ENOMEM, ENOBUFS, ... */
                                 assert(errno != EBADF);
-                                fprintf(stderr, "read: %m\n");
+                                perror("read");
                                 return h1_close(h1);
                         }
                 }
@@ -1142,7 +1153,7 @@ static void h1d_unlink(struct mw_h1d *h1d, bool do_close)
         if (h1d->lfd < 0 || !h1d->pid_len)
                 return;
         if (getsockname(h1d->lfd, &sa.any, &len) < 0) {
-                fprintf(stderr, "getsockname: %m\n");
+                perror("getsockname");
                 return;
         }
         if (do_close) { /* only safe to close if thread isn't running */
@@ -1208,13 +1219,13 @@ static int h1d_init(struct mw_h1d *h1d, const char *menv)
                 return fprintf(stderr, "unlink(%s): %m\n", sa.un.sun_path);
         h1d->lfd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
         if (h1d->lfd < 0)
-                return fprintf(stderr, "socket: %m\n");
+                return perror("socket"), 1;
         if (bind(h1d->lfd, &sa.any, (socklen_t)sizeof(sa)) < 0) {
-                fprintf(stderr, "bind: %m\n");
+                perror("bind");
                 goto close_fail;
         }
         if (listen(h1d->lfd, 1024) < 0) {
-                fprintf(stderr, "listen: %m\n");
+                perror("listen");
                 goto close_fail;
         }
         h1d->alive = 1; /* runs in parent, before pthread_create */
diff --git a/ext/mwrap/mwrap_core.h b/ext/mwrap/mwrap_core.h
index 827ee7b..a84cd6d 100644
--- a/ext/mwrap/mwrap_core.h
+++ b/ext/mwrap/mwrap_core.h
@@ -4,7 +4,9 @@
  * Disclaimer: I don't really know my way around XS or Perl internals well
  */
 #define _LGPL_SOURCE /* allows URCU to inline some stuff */
-#define _GNU_SOURCE
+#ifndef _GNU_SOURCE
+#        define _GNU_SOURCE
+#endif
 #include "mymalloc.h" /* includes dlmalloc_c.h */
 #ifndef MWRAP_PERL
 #        define MWRAP_PERL 0
@@ -19,9 +21,6 @@
 #        define        MWRAP_BT_MAX 32
 #endif
 
-#ifndef _GNU_SOURCE
-#        define _GNU_SOURCE
-#endif
 #include <execinfo.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -389,11 +388,8 @@ static const COP *mwp_curcop(void)
 static const char *mw_perl_src_file_cstr(unsigned *lineno)
 {
         const COP *cop = mwp_curcop();
-        if (!cop) return NULL;
-        const char *fn = CopFILE(cop);
-        if (!fn) return NULL;
-        *lineno = CopLINE(cop);
-        return fn;
+        *lineno = cop ? CopLINE(cop) : 0;
+        return cop ? CopFILE(cop) : NULL;
 }
 #        define SRC_FILE_CSTR(lineno) mw_perl_src_file_cstr(lineno)
 #endif /* MWRAP_PERL */
@@ -735,6 +731,7 @@ enomem:
 struct dump_arg {
         FILE *fp;
         size_t min;
+        bool dump_csv;
 };
 
 char **bt_syms(void * const *addrlist, uint32_t size)
@@ -745,7 +742,7 @@ char **bt_syms(void * const *addrlist, uint32_t size)
 #else /* make FreeBSD look like glibc output: */
         char **s = backtrace_symbols_fmt(addrlist, size, "%f(%n%D) [%a]");
 #endif
-        if (!s) fprintf(stderr, "backtrace_symbols: %m\n");
+        if (!s) perror("backtrace_symbols");
         return s;
 }
 
@@ -757,12 +754,16 @@ static void cleanup_free(void *any)
         free(*p);
 }
 
+static void *write_csv(FILE *, size_t min, const char *sort, size_t sort_len);
 static void *dump_to_file(struct dump_arg *a)
 {
         struct cds_lfht_iter iter;
         struct src_loc *l;
         struct cds_lfht *t;
 
+        if (a->dump_csv)
+                return write_csv(a->fp, a->min, NULL, 0);
+
         ++locating;
         rcu_read_lock();
         t = CMM_LOAD_SHARED(totals);
@@ -860,7 +861,7 @@ __attribute__ ((destructor)) static void mwrap_dtor(void)
 {
         const char *opt = getenv("MWRAP");
         const char *modes[] = { "a", "a+", "w", "w+", "r+" };
-        struct dump_arg a = { .min = 0 };
+        struct dump_arg a = { .min = 0, .dump_csv = false };
         size_t i;
         int dump_fd;
         char *dump_path;
@@ -873,27 +874,64 @@ __attribute__ ((destructor)) static void mwrap_dtor(void)
                 return;
 
         ++locating;
-        if ((dump_path = strstr(opt, "dump_path:")) &&
-                        (dump_path += sizeof("dump_path")) &&
-                        *dump_path) {
+
+        /* parse dump_csv:$PATHNAME */
+        if ((dump_path = strstr(opt, "dump_csv:"))) {
+                dump_path += sizeof("dump_csv");
+                if (!*dump_path)
+                        dump_path = NULL;
+                else
+                        a.dump_csv = true;
+        }
+        if (!dump_path) {
+                /* parse dump_path:$PATHNAME */
+                if ((dump_path = strstr(opt, "dump_path:"))) {
+                        dump_path += sizeof("dump_path");
+                        if (!*dump_path)
+                                dump_path = NULL;
+                }
+        }
+        if (dump_path) {
                 char *end = strchr(dump_path, ',');
                 char buf[PATH_MAX];
+                AUTO_FREE char *pid_path = NULL;
                 if (end) {
                         mwrap_assert((end - dump_path) < (intptr_t)sizeof(buf));
                         end = mempcpy(buf, dump_path, end - dump_path);
                         *end = 0;
                         dump_path = buf;
                 }
+
+                /* %p => PID expansion (Linux core_pattern uses %p, too) */
+                if ((s = strchr(dump_path, '%')) && s[1] == 'p' &&
+                                /* don't allow injecting extra formats: */
+                                !strchr(s + 2, '%')) {
+                        s[1] = 'd'; /* s/%p/%d/ to make asprintf happy */
+                        int n = asprintf(&pid_path, dump_path, (int)getpid());
+                        if (n < 0)
+                                fprintf(stderr,
+                                        "asprintf failed: %m, dumping to %s\n",
+                                        dump_path);
+                        else
+                                dump_path = pid_path;
+                }
                 dump_fd = open(dump_path, O_CLOEXEC|O_WRONLY|O_APPEND|O_CREAT,
                                 0666);
                 if (dump_fd < 0) {
                         fprintf(stderr, "open %s failed: %m\n", dump_path);
                         goto out;
                 }
+        } else {
+                s = strstr(opt, "dump_fd:");
+                if (!s)
+                        goto out;
+                if (!sscanf(s, "dump_fd:%d", &dump_fd))
+                        goto out;
         }
-        else if (!sscanf(opt, "dump_fd:%d", &dump_fd))
-                goto out;
 
+        /* allow dump_csv standalone for dump_fd */
+        if (!a.dump_csv && strstr(opt, "dump_csv"))
+                a.dump_csv = true;
         if ((s = strstr(opt, "dump_min:")))
                 sscanf(s, "dump_min:%zu", &a.min);
 
@@ -1019,7 +1057,7 @@ __attribute__((constructor)) static void mwrap_ctor(void)
                 h->real = h;
                 call_rcu(&h->as.dead, free_hdr_rcu);
         } else
-                fprintf(stderr, "malloc: %m\n");
+                perror("malloc");
 
         h1d_start();
         CHECK(int, 0, pthread_sigmask(SIG_SETMASK, &old, NULL));