** Description changed:
[Impact]
The `libm.a` static library on i386 architecture lacks the math function
`fmod`. This will break static compilation in scenarios where programs expect
the function to exist.
- (mantic-i386)$ readelf --syms --wide /usr/lib/i386-linux-gnu/libm.a | grep
fmod
+ The commit https://sourceware.org/git/?p=glibc.git;a=commit;h=16439f419b
+ removed the static fmod/fmodf on i386 (and m68k) with an empty w_fmod.c
+ used by ABIs that rely on the newer implementation. However, this change
+ also removed the necessary symbols from the static library. As a side
+ effect, the expected compatibility symbols were no longer emitted into
+ the static library.
+
+ As a consequence, static builds that reference fmod may fail with
+ unresolved symbol errors during the linking stage.
+
+
+ [Test Case]
+
+ On a noble host install libc6-dev:i386 (and clang if needed) package. In
+ the test using clang with the -m32 flag in order to ignore the 64-bit
+ hardware and build this as a 32-bit executable since the bus is
+ affecting these architectures.
+
+ Verify afterwards:
+ $ ls /usr/lib32/libm.a
+ # confirm the library architecture
+ file /usr/lib32/libm.a
+ /usr/lib32/libm.a: current ar archive
+
+
+ Create a simple test.c file with the following contents:
+
+ #include <math.h>
+
+ int main() {
+ return fmod(5.0, 2.0);
+ }
+
+ [BEFORE THE PATCH]
+
+ Compile statically using clang:
+ $ clang -m32 -static test.c -lm
+ /usr/bin/ld: /tmp/test-6f7fbc.o: in function `main':
+ test.c:(.text+0x38): undefined reference to `fmod'
+ clang: error: linker command failed with exit code 1 (use -v to see
invocation)
+
+ Check if the symbol is present:
+ $ readelf --syms --wide /usr/lib/i386-linux-gnu/libm.a | grep fmod
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodl_compat.o)
File: /usr/lib/i386-linux-gnu/libm.a(w_fmod_compat.o)
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodf_compat.o)
File: /usr/lib/i386-linux-gnu/libm.a(e_fmodl.o)
2: 00000000 23 FUNC GLOBAL DEFAULT 1 __ieee754_fmodl
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodl.o)
4: 00000000 148 FUNC GLOBAL DEFAULT 2 __fmodl
7: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodl
9: 00000000 148 FUNC WEAK DEFAULT 2 fmodf64x
10: 00000000 148 FUNC WEAK DEFAULT 2 fmodl
File: /usr/lib/i386-linux-gnu/libm.a(e_fmod.o)
2: 00000000 23 FUNC GLOBAL DEFAULT 1 __ieee754_fmod
File: /usr/lib/i386-linux-gnu/libm.a(w_fmod.o)
File: /usr/lib/i386-linux-gnu/libm.a(e_fmodf.o)
2: 00000000 23 FUNC GLOBAL DEFAULT 1 __ieee754_fmodf
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodf.o)
File: /usr/lib/i386-linux-gnu/libm.a(e_fmodf128.o)
7: 00000000 3227 FUNC GLOBAL DEFAULT 2 __ieee754_fmodf128
13: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodf128
14: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodf128
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodf128.o)
6: 00000000 578 FUNC GLOBAL DEFAULT 2 __fmodf128
10: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodf128
12: 00000000 578 FUNC WEAK DEFAULT 2 fmodf128
- [Test Case]
- On a noble host install libc6-dev:i386 package and
+ Without the fix, fmod function is not present in the binary. This indicates
that the linker was unable to resolve the fmod symbol from the static math
library during the linking stage.
- $ readelf --syms --wide /usr/lib/i386-linux-gnu/libm.a | grep fmod
- Without the fix fmod function is not present (see readelf output of
- Description).
+ [AFTER THE PATCH]
- With the fix fmod fuctions are present:
+ Try again to statically compile the test.c program from above:
+ $ clang -m32 -static test.c -lm
+
+ It should work without any errors and have a “a.out” file.
+
+ This resolves the "undefined reference to fmod" error, ensuring that the
+ necessary math functions from the libm library are properly linked and
+ included in the static binary.
+
+ In addition, with the fix fmod fuctions are present:
readelf --syms --wide /usr/lib/i386-linux-gnu/libm.a | grep fmod
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodl_compat.o)
File: /usr/lib/i386-linux-gnu/libm.a(w_fmod_compat.o)
4: 00000000 122 FUNC GLOBAL DEFAULT 2 __fmod
7: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmod
9: 00000000 122 FUNC WEAK DEFAULT 2 fmodf32x
10: 00000000 122 FUNC WEAK DEFAULT 2 fmodf64
11: 00000000 122 FUNC WEAK DEFAULT 2 fmod
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodf_compat.o)
4: 00000000 114 FUNC GLOBAL DEFAULT 2 __fmodf
7: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodf
9: 00000000 114 FUNC WEAK DEFAULT 2 fmodf32
10: 00000000 114 FUNC WEAK DEFAULT 2 fmodf
File: /usr/lib/i386-linux-gnu/libm.a(e_fmodl.o)
2: 00000000 23 FUNC GLOBAL DEFAULT 1 __ieee754_fmodl
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodl.o)
4: 00000000 148 FUNC GLOBAL DEFAULT 2 __fmodl
7: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodl
9: 00000000 148 FUNC WEAK DEFAULT 2 fmodf64x
10: 00000000 148 FUNC WEAK DEFAULT 2 fmodl
File: /usr/lib/i386-linux-gnu/libm.a(e_fmod.o)
2: 00000000 19 FUNC GLOBAL DEFAULT 1 __ieee754_fmod
File: /usr/lib/i386-linux-gnu/libm.a(w_fmod.o)
File: /usr/lib/i386-linux-gnu/libm.a(e_fmodf.o)
2: 00000000 19 FUNC GLOBAL DEFAULT 1 __ieee754_fmodf
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodf.o)
File: /usr/lib/i386-linux-gnu/libm.a(e_fmodf128.o)
7: 00000000 3227 FUNC GLOBAL DEFAULT 2 __ieee754_fmodf128
13: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodf128
14: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodf128
File: /usr/lib/i386-linux-gnu/libm.a(w_fmodf128.o)
6: 00000000 578 FUNC GLOBAL DEFAULT 2 __fmodf128
10: 00000000 0 NOTYPE GLOBAL DEFAULT UND __ieee754_fmodf128
12: 00000000 578 FUNC WEAK DEFAULT 2 fmodf128
[Regression Potential]
The patch adds the symbols fmod/fmodf for static builds for i386 and m68k.
The changes are arch specific, so any regression would affect i386 and m68k
for the static libm.a.
[Other]
Fix :
https://sourceware.org/git/?p=glibc.git;a=commit;h=0b716305dfb48c2d13ed4f7d06c082b90c1d226f
Affected Ubuntu releases : Noble
** Changed in: glibc (Ubuntu Noble)
Status: Incomplete => In Progress
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https://bugs.launchpad.net/bugs/2036283
Title:
i386 glibc is missing fmod in libm.a
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