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Date: Mon, 21 Jan 2019 18:57:53 +0100
From: Florian Weimer <fweimer@...hat.com>
To: musl@...ts.openwall.com
Subject: Symbol versioning approximation trips on compat symbols
On what appears to be current Alpine Linux (musl-1.1.19-r10), the
following reproducer
######################################################################
cat > symver.c <<EOF
void
compat_function (void)
{
}
__asm__ (".symver compat_function,compat_function@...VER");
void
call_compat_function (void)
{
return compat_function ();
}
EOF
echo "SYMVER { };" > symver.map
cat > main.c <<EOF
extern void call_compat_function (void);
int
main (void)
{
call_compat_function ();
}
EOF
gcc -fpic -shared -o symver.so -Wl,--version-script=symver.map symver.c
gcc -Wl,--rpath=. -o main main.c symver.so
######################################################################
fails with:
$ ./main
Error relocating ./symver.so: compat_function: symbol not found
The problem is the compatibility symbol (one @ instead of @@). The
dynamic linker is supposed to ignore the difference between the two, the
default vs non-default version only matters to the link editor when
processing an undefined symbol without a symbol version.
In my case, I do not need symbol interposition and therefore can work
around this, but I wonder if there is some sort of approved compile-time
or link-time check to detect this issue. Unfortunately, the Alpine
Linux toolchain (and part of the system) is built *with* symbol
versioning support, so this does not appear to be straightforward.
The actual application does not need to make the symbol interposable, so
I can use a hidden alias within the DSO for PLT avoidance (and more
configure checks to disable all this on targets which do not support
*that*).
Thanks,
Florian
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