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LibELF: Fix calculation for TLS relocations

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The calculation for TLS relocations was incorrect which would
result in overlapping TLS variables when more than one shared
object used TLS variables.

This bug can be reproduced with a shared library and a program
like this:

    $ cat tlstest.c
    #include <string.h>
    __thread char tls_val[1024];
    void set_val() { memset(tls_val, 0, sizeof(tls_val)); }

    $ gcc -g -shared -o usr/lib/libtlstest.so tlstest.c

    $ cat test.c
    void set_val();
    int main() { set_val(); }
    $ gcc -g -o tls test.c -ltlstest

Due to the way the TLS relocations are done this program would
clobber libc's TLS variables (e.g. errno).
This commit is contained in:
Gunnar Beutner 2021-04-19 11:00:06 +02:00 committed by Andreas Kling
parent 0cca23def5
commit c32b58873a
Notes: sideshowbarker 2024-07-18 19:24:25 +09:00 
Author: https://github.com/gunnarbeutner
Commit: https://github.com/SerenityOS/serenity/commit/c32b58873a0
Pull-request: https://github.com/SerenityOS/serenity/pull/6480
1 changed files with 1 additions and 2 deletions
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3
Userland/Libraries/LibELF/DynamicLoader.cpp
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@ -498,8 +498,7 @@ DynamicLoader::RelocationResult DynamicLoader::do_relocation(size_t total_tls_si
u32 symbol_value = res.value().value;
auto* dynamic_object_of_symbol = res.value().dynamic_object;
VERIFY(dynamic_object_of_symbol);
size_t offset_of_tls_end = dynamic_object_of_symbol->tls_offset().value() + dynamic_object_of_symbol->tls_size().value();
*patch_ptr = (offset_of_tls_end - total_tls_size - symbol_value - sizeof(Elf32_Addr));
*patch_ptr = dynamic_object_of_symbol->tls_offset().value() + symbol_value - total_tls_size;
break;
}
case R_386_JMP_SLOT: {