| Summary: | Debugger hangs on a shared library in memory-mapped file. | ||
|---|---|---|---|
| Product: | gdb | Reporter: | Marcin Copik <mcopik> |
| Component: | shlibs | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | NEW --- | ||
| Severity: | normal | CC: | asaffisher.dev, ppluzhnikov |
| Priority: | P2 | ||
| Version: | 12.1 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | 2024-08-27 00:00:00 | |
|
Description
Marcin Copik
2022-09-19 13:03:04 UTC
The reason this happens is because /proc/self is different between inferior and GDB. I proposed a patch to fix it today. I just hit this as well. Trivial repro with current trunk:
--- foo.c ---
#include <assert.h>
int fn (int x)
{
assert (x > 0);
return x + 1;
}
--- main1.c ---
#include <dlfcn.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
int fd = open("./foo.so", O_RDONLY);
char path[1024];
sprintf(path, "/proc/self/fd/%d", fd);
fprintf (stderr, "Before dlopen %s\n", path);
void *h = dlopen(path, RTLD_LOCAL|RTLD_LAZY);
int (*fn)(int) = dlsym(h, "fn");
fprintf (stderr, "Before call to fn\n");
return fn(0);
}
gcc -g -fPIC -shared -o foo.so foo.c &&
gcc -g main1.c -ldl && ./a.out
Before dlopen /proc/self/fd/3
Before call to fn
a.out: foo.c:5: fn: Assertion `x > 0' failed.
Aborted
---
Everything is as expected up to this point
gdb/gdb -q -ex run ./a.out
Reading symbols from ./a.out...
Starting program: /tmp/memfd/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Before dlopen /proc/self/fd/3
... GDB hangs forever trying to read from some pipe, and is blocking all signals requiring that I pkill -9 from another terminal.
strace -p $(pgrep gdb)
strace: Process 3885955 attached
read(16, ^Cstrace: Process 3885955 detached
<detached ...>
ls -l /proc/3885955/fd/16
lr-x------ 1 ppluzhnikov primarygroup 64 Aug 27 03:43 /proc/3885955/fd/16 -> 'pipe:[95221642]'
---
It's also easy to make GDB not hang, but simply fail to load symbols:
--- main.c ---
#include <assert.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
int fd = open("./foo.so", O_RDONLY);
char path[1024];
assert(dup2(fd, 133) != -1);
sprintf(path, "/proc/self/fd/%d", 133);
void *h = dlopen(path, RTLD_LOCAL|RTLD_LAZY);
int (*fn)(int) = dlsym(h, "fn");
return fn(0);
}
gcc -g main.c -ldl &&
gdb/gdb -q -ex run ./a.out
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
warning: Could not load shared library symbols for /proc/self/fd/133.
Do you need "set solib-search-path" or "set sysroot"?
a.out: foo.c:5: fn: Assertion `x > 0' failed.
Program received signal SIGABRT, Aborted.
0x00007ffff7e520ec in ?? () from /lib/x86_64-linux-gnu/libc.so.6
(gdb) bt
#0 0x00007ffff7e520ec in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x00007ffff7e04102 in raise () from /lib/x86_64-linux-gnu/libc.so.6
#2 0x00007ffff7ded4f2 in abort () from /lib/x86_64-linux-gnu/libc.so.6
#3 0x00007ffff7ded415 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#4 0x00007ffff7dfcd32 in __assert_fail () from /lib/x86_64-linux-gnu/libc.so.6
#5 0x00007ffff7fbf142 in ?? ()
#6 0x00007fffffffd868 in ?? ()
#7 0x00000000ffffd868 in ?? ()
#8 0x00007fffffffd750 in ?? ()
#9 0x000055555555524c in main () at main.c:18
Backtrace stopped: frame did not save the PC
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