On 08/29/2014 12:29 PM, Mikulas Patocka wrote: > I found out that the patch cc75d373fdb9668f367959f99f0b67e056a6c18a > (Enable secureplt by default for alpha-linux) committed to binutils git > breaks ld on alpha. > > This is a minimalized testcase that shows the breakage: > http://people.redhat.com/~mpatocka/testcases/alpha-ld-bug/ld-bug.tar.xz > > To reproduce the bug, run ./ld-bug.sh to perform the linking, then run the > resulting binary: > LD_PRELOAD=./libots.so ./memset
Incidentally, you can't package your ld.so and libc.so and then use the system ld.so. The ld.so and libc.so used must match. That said, removing the stuff redundant with my system libraries I can reproduce the crash. > The bug happens when using the Compaq C Compiler (ccc) on Alpha Linux (it > can be downloaded from > ftp://ftp.compaq.com/pub/products/C-CXX/linux/compaq_c/ ). When using > optimization, Compaq C replaces a call to memset with a call to _OtsZero > located in libots.so. The above patch breaks ld in such a way that the > resulting program crashes when performing the dynamic call to _OtsZero. The code that ccc is generating is incorrect: 1c: 00 40 5b 6b jsr ra,(t12),20 <main+0x20> 1c: LITUSE printf+0x3 1c: HINT printf 20: 00 00 ba 27 ldah gp,0(ra) 20: GPDISP *ABS*+0x8 24: 90 01 3f 22 lda a1,400 28: 00 00 bd 23 lda gp,0(gp) 2c: 00 00 7d a7 ldq t12,0(gp) 2c: ELF_LITERAL _OtsZero 30: 00 00 1d a6 ldq a0,0(gp) 30: ELF_LITERAL a 34: 00 00 1d a4 ldq v0,0(gp) 34: ELF_LITERAL .data 38: 00 00 fe 2f unop 3c: 00 40 5b 6b jsr ra,(t12),40 <main+0x40> 3c: LITUSE _OtsZero+0x3 3c: HINT _OtsZero 40: 00 00 7d a7 ldq t12,0(gp) 40: ELF_LITERAL printf 44: 10 00 00 22 lda a0,16(v0) 44: LITUSE .data+0x1 48: 00 00 fe 2f unop 4c: 00 40 5b 6b jsr ra,(t12),50 <main+0x50> 4c: LITUSE printf+0x3 4c: HINT printf At 0x40, the compiler has failed to reload gp after the call, like it did after the first call to printf at 0x20. The Compaq compiler seems to be assuming non-standard calling conventions in the call to _OtsZero. If you force LD_BIND_NOW=1 so that all relocation happens first, the program does run correctly. There are several ways libots could have been written to annotate the function for non-standard calling conventions. But Compaq probably went under before that bug was exposed. Assuming that one can't get the source, it may be possible to modify the libots.so binary so that it works with modern linkers. This is not a bug in ld, per se. r~ _______________________________________________ bug-binutils mailing list bug-binutils@gnu.org https://lists.gnu.org/mailman/listinfo/bug-binutils
