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1beb39086c
The SystemZ linkers provide an optimization to transform a general- or local-dynamic TLS sequence into an initial-exec sequence if possible. Do do that, the compiler generates a function call to __tls_get_offset, which is a brasl instruction annotated with *two* relocations: - a R_390_PLT32DBL to install __tls_get_offset as branch target - a R_390_TLS_GDCALL / R_390_TLS_LDCALL to inform the linker that the TLS optimization should be performed if possible If the optimization is performed, the brasl is replaced by an ld load instruction. However, *both* relocs are processed independently by the linker. Therefore it is crucial that the R_390_PLT32DBL is processed *first* (installing the branch target for the brasl) and the R_390_TLS_GDCALL is processed *second* (replacing the whole brasl with an ld). If the relocs are swapped, the linker will first replace the brasl with an ld, and *then* install the __tls_get_offset branch target offset. Since ld has a different layout than brasl, this may even result in a completely different (or invalid) instruction; in any case, the resulting code is corrupted. Unfortunately, the way the MC common code sorts relocations causes these two to *always* end up the wrong way around, resulting in wrong code generation by the linker and crashes. This patch overrides the sortRelocs routine to detect this particular pair of relocs and enforce the required order. llvm-svn: 255787 |
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