[Bug libc/31730] New: backtrace_symbols_fd prints different strings than backtrace_symbols returns

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31730

            Bug ID: 31730
           Summary: backtrace_symbols_fd prints different strings than
                    backtrace_symbols returns
           Product: glibc
           Version: 2.39
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: bruno at clisp dot org
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Created attachment 15516
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15516&action=edit
test case foo.c

The documentation of backtrace_symbols_fd in
https://www.gnu.org/software/libc/manual/html_node/Backtraces.html says: "The
backtrace_symbols_fd function performs the same translation as the function
backtrace_symbols function. Instead of returning the strings to the caller, it
writes the strings to the file descriptor fd, one per line."

But in glibc 2.39, it prints different strings.

How to reproduce:
============================= foo.c =============================
#include <execinfo.h>
#include <stdio.h>
#include <stdlib.h>

static void
test_backtrace (void)
{
  void *buffer[10];
  int size;
  char **symbols;

  size = backtrace (buffer, 10);

  backtrace_symbols_fd (buffer, size, 1);
  printf ("\n");

  symbols = backtrace_symbols (buffer, size);
  if (symbols != NULL)
    {
      for (int i = 0; i < size; ++i)
        printf ("%s\n", symbols[i]);
      free (symbols);
    }
}

int
main (void)
{
  test_backtrace ();
}
================================================================
$ gcc -Wall foo.c
$ ./a.out
./a.out[0x40118f]
./a.out[0x40121a]
/lib64/libc.so.6(+0x2a088)[0x7fc7bf945088]
/lib64/libc.so.6(__libc_start_main+0x8b)[0x7fc7bf94514b]
./a.out[0x4010b5]

./a.out() [0x40118f]
./a.out() [0x40121a]
/lib64/libc.so.6(+0x2a088) [0x7fc7bf945088]
/lib64/libc.so.6(__libc_start_main+0x8b) [0x7fc7bf94514b]
./a.out() [0x4010b5]

As you can see, the strings printed by backtrace_symbols_fd lack
1. a substring "()" when the offset is not known,
2. a space before the '[' character.

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