DEV: gdb: add a new utility to extract libs from a core dump: libs-from-core

This utility takes in argument the path to a core dump, and it looks
for the archive signature of libraries embedded with "set-dumpable libs",
and either emits the offset and size of stdout, or directly dumps the
contents so that the tar file can be extracted directly by piping the
output to tar xf.

diff --git a/Makefile b/Makefile
index aae8f863e789675ddef3e0c32ba28275db5b3611..b72189e9886531cc8e8ac360eaf2f5b0435a5285 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -1043,7 +1043,7 @@ IGNORE_OPTS=help install install-man install-doc install-bin \
        uninstall clean tags cscope tar git-tar version update-version \
        opts reg-tests reg-tests-help unit-tests admin/halog/halog dev/flags/flags \
        dev/haring/haring dev/ncpu/ncpu dev/poll/poll dev/tcploop/tcploop \
-       dev/term_events/term_events dev/gdb/pm-from-core
+       dev/term_events/term_events dev/gdb/pm-from-core dev/gdb/libs-from-core
 
 ifneq ($(TARGET),)
 ifeq ($(filter $(firstword $(MAKECMDGOALS)),$(IGNORE_OPTS)),)
@@ -1077,6 +1077,9 @@ admin/dyncookie/dyncookie: admin/dyncookie/dyncookie.o
 dev/flags/flags: dev/flags/flags.o
        $(cmd_LD) $(ARCH_FLAGS) $(LDFLAGS) -o $@ $^ $(LDOPTS)
 
+dev/gdb/libs-from-core: dev/gdb/libs-from-core.o
+       $(cmd_LD) $(ARCH_FLAGS) $(LDFLAGS) -o $@ $^ $(LDOPTS)
+
 dev/gdb/pm-from-core: dev/gdb/pm-from-core.o
        $(cmd_LD) $(ARCH_FLAGS) $(LDFLAGS) -o $@ $^ $(LDOPTS)
 
@@ -1178,7 +1181,7 @@ distclean: clean
        $(Q)rm -f admin/dyncookie/dyncookie
        $(Q)rm -f dev/haring/haring dev/ncpu/ncpu{,.so} dev/poll/poll dev/tcploop/tcploop
        $(Q)rm -f dev/hpack/decode dev/hpack/gen-enc dev/hpack/gen-rht
-       $(Q)rm -f dev/qpack/decode dev/gdb/pm-from-core
+       $(Q)rm -f dev/qpack/decode dev/gdb/pm-from-core dev/gdb/libs-from-core
 
 tags:
        $(Q)find src include \( -name '*.c' -o -name '*.h' \) -print0 | \

diff --git a/dev/gdb/libs-from-core.c b/dev/gdb/libs-from-core.c
new file mode 100644 (file)
index 0000000..9da8561
--- /dev/null
+++ b/dev/gdb/libs-from-core.c
@@ -0,0 +1,162 @@
+/*
+ * Extracts the libs archives from a core dump
+ *
+ * Copyright (C) 2026 Willy Tarreau <w@1wt.eu>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+/* Note: builds with no option under glibc, and can be built as a minimal
+ * uploadable static executable using nolibc as well:
+    gcc -o libs-from-core -nostdinc -nostdlib -s -Os -static -fno-ident \
+        -fno-exceptions -fno-asynchronous-unwind-tables -fno-unwind-tables \
+        -Wl,--gc-sections,--orphan-handling=discard,-znoseparate-code \
+        -I /path/to/nolibc-sysroot/include libs-from-core.c
+ */
+#define _GNU_SOURCE
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <elf.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+void usage(const char *progname)
+{
+       const char *slash = strrchr(progname, '/');
+
+       if (slash)
+               progname = slash + 1;
+
+       fprintf(stderr,
+               "Usage: %s [-q] <core_file>\n"
+               "Locate a libs archive from an haproxy core dump and dump it to stdout.\n"
+               "Arguments:\n"
+               "    -q            Query mode: only report offset and length, do not dump\n"
+               "    core_file     Core dump produced by haproxy\n",
+               progname);
+}
+
+int main(int argc, char **argv)
+{
+       Elf64_Ehdr *ehdr;
+       Elf64_Phdr *phdr;
+       struct stat st;
+       uint8_t *mem;
+       int i, fd;
+       const char *fname;
+       int quiet = 0;
+       int arg;
+
+       for (arg = 1; arg < argc; arg++) {
+               if (*argv[arg] != '-')
+                       break;
+
+               if (strcmp(argv[arg], "-q") == 0)
+                       quiet = 1;
+               else if (strcmp(argv[arg], "--") == 0) {
+                       arg++;
+                       break;
+               }
+       }
+
+       if (arg < argc) {
+               fname = argv[arg];
+       } else {
+               usage(argv[0]);
+               exit(1);
+       }
+
+       fd = open(fname, O_RDONLY);
+
+       /* Let's just map the core dump as an ELF header */
+       fstat(fd, &st);
+       mem = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+       if (mem == MAP_FAILED) {
+               perror("mmap()");
+               exit(1);
+       }
+
+       /* get the program headers */
+       ehdr = (Elf64_Ehdr *)mem;
+
+       /* check that it's really a core. Should be "\x7fELF" */
+       if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0) {
+               fprintf(stderr, "ELF magic not found.\n");
+               exit(1);
+       }
+
+       if (ehdr->e_ident[EI_CLASS] != ELFCLASS64) {
+               fprintf(stderr, "Only 64-bit ELF supported.\n");
+               exit(1);
+       }
+
+       if (ehdr->e_type != ET_CORE) {
+               fprintf(stderr, "ELF type %d, not a core dump.\n", ehdr->e_type);
+               exit(1);
+       }
+
+       /* OK we can safely go with program headers */
+       phdr = (Elf64_Phdr *)(mem + ehdr->e_phoff);
+
+       for (i = 0; i < ehdr->e_phnum; i++) {
+               uint64_t size   = phdr[i].p_filesz;
+               uint64_t offset = phdr[i].p_offset;
+               int ret = 0;
+
+               if (phdr[i].p_type != PT_LOAD)
+                       continue;
+
+               //fprintf(stderr, "Scanning segment %d...\n", ehdr->e_phnum);
+               //fprintf(stderr, "\r%-5d: off=%lx va=%lx sz=%lx     ", i, (long)offset, (long)phdr[i].p_vaddr, (long)size);
+               if (!size)
+                       continue;
+
+               if (size < 512) // minimum for a tar header
+                       continue;
+
+               /* tar magic */
+               if (memcmp(mem + offset + 257, "ustar\0""00", 8) != 0)
+                       continue;
+
+               /* uid, gid */
+               if (memcmp(mem + offset + 108, "0000000\0""0000000\0", 16) != 0)
+                       continue;
+
+               /* link name */
+               if (memcmp(mem + offset + 157, "haproxy-libs-dump\0", 18) != 0)
+                       continue;
+
+               /* OK that's really it */
+
+               if (quiet)
+                       printf("offset=%#lx size=%#lx\n", offset, size);
+               else
+                       ret = (write(1, mem + offset, size) == size) ? 0 : 1;
+               return ret;
+       }
+       //fprintf(stderr, "\r%75s\n", "\r");
+       fprintf(stderr, "libs archive not found. Was 'set-dumpable' set to 'libs' ?\n");
+       return 1;
+}