From: Ian Lance Taylor <iant@golang.org>
To: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: libbacktrace patch committed: Don't assume compressed section aligned
Date: Fri, 8 Mar 2024 13:57:22 -0800 [thread overview]
Message-ID: <CAOyqgcUVTs3MQKg7a-JPBXVrHh7LxkiwjuPo_9gcqFV1x9aROg@mail.gmail.com> (raw)
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Reportedly when lld compresses debug sections, it fails to set the
alignment of the compressed section such that the compressed header
can be read directly. To me this seems like a bug in lld. However,
libbacktrace needs to work around it. This patch, originally by the
GitHub user ubyte, does that. Bootstrapped and tested on
x86_64-pc-linux-gnu. Committed to mainline.
Ian
* elf.c (elf_uncompress_chdr): Don't assume compressed section is
aligned.
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5825bd0e0d0040126e78269e56c9b9f533e2a520
diff --git a/libbacktrace/elf.c b/libbacktrace/elf.c
index 7841c86cd9c..3cd87020b03 100644
--- a/libbacktrace/elf.c
+++ b/libbacktrace/elf.c
@@ -5076,7 +5076,7 @@ elf_uncompress_chdr (struct backtrace_state *state,
backtrace_error_callback error_callback, void *data,
unsigned char **uncompressed, size_t *uncompressed_size)
{
- const b_elf_chdr *chdr;
+ b_elf_chdr chdr;
char *alc;
size_t alc_len;
unsigned char *po;
@@ -5088,27 +5088,30 @@ elf_uncompress_chdr (struct backtrace_state *state,
if (compressed_size < sizeof (b_elf_chdr))
return 1;
- chdr = (const b_elf_chdr *) compressed;
+ /* The lld linker can misalign a compressed section, so we can't safely read
+ the fields directly as we can for other ELF sections. See
+ https://github.com/ianlancetaylor/libbacktrace/pull/120. */
+ memcpy (&chdr, compressed, sizeof (b_elf_chdr));
alc = NULL;
alc_len = 0;
- if (*uncompressed != NULL && *uncompressed_size >= chdr->ch_size)
+ if (*uncompressed != NULL && *uncompressed_size >= chdr.ch_size)
po = *uncompressed;
else
{
- alc_len = chdr->ch_size;
+ alc_len = chdr.ch_size;
alc = backtrace_alloc (state, alc_len, error_callback, data);
if (alc == NULL)
return 0;
po = (unsigned char *) alc;
}
- switch (chdr->ch_type)
+ switch (chdr.ch_type)
{
case ELFCOMPRESS_ZLIB:
if (!elf_zlib_inflate_and_verify (compressed + sizeof (b_elf_chdr),
compressed_size - sizeof (b_elf_chdr),
- zdebug_table, po, chdr->ch_size))
+ zdebug_table, po, chdr.ch_size))
goto skip;
break;
@@ -5116,7 +5119,7 @@ elf_uncompress_chdr (struct backtrace_state *state,
if (!elf_zstd_decompress (compressed + sizeof (b_elf_chdr),
compressed_size - sizeof (b_elf_chdr),
(unsigned char *)zdebug_table, po,
- chdr->ch_size))
+ chdr.ch_size))
goto skip;
break;
@@ -5126,7 +5129,7 @@ elf_uncompress_chdr (struct backtrace_state *state,
}
*uncompressed = po;
- *uncompressed_size = chdr->ch_size;
+ *uncompressed_size = chdr.ch_size;
return 1;
@@ -6876,8 +6879,8 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
}
}
- // A debuginfo file may not have a useful .opd section, but we can use the
- // one from the original executable.
+ /* A debuginfo file may not have a useful .opd section, but we can use the
+ one from the original executable. */
if (opd == NULL)
opd = caller_opd;
next reply other threads:[~2024-03-08 21:57 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-08 21:57 Ian Lance Taylor [this message]
2024-03-08 22:47 ` Fangrui Song
2024-03-09 3:27 ` H.J. Lu
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