| Message ID | alpine.DEB.2.20.17.1611231217350.10580@tp.orcam.me.uk |
|---|---|
| State | Accepted |
| Headers | show |
On Wed, 23 Nov 2016, Maciej W. Rozycki wrote: > In a microMIPS compilation of `.init' code use the R_MICROMIPS_JALR > relocation intended for PIC call relaxation in microMIPS code rather > than the corresponding R_MIPS_JALR relocation meant for regular MIPS > code only. > > * sysdeps/mips/mips32/crti.S (JALR_RELOC): New macro. > (_init): Use it in place of hardcoded R_MIPS_JALR. > * sysdeps/mips/mips64/n32/crti.S (JALR_RELOC): New macro. > (_init): Use it in place of hardcoded R_MIPS_JALR. > * sysdeps/mips/mips64/n64/crti.S (JALR_RELOC): New macro. > (_init): Use it in place of hardcoded R_MIPS_JALR. > --- > No regressions with the `mips-mti-linux-gnu' target in o32 regular MIPS > and microMIPS multilib testing and neither in n32 and n64 regular MIPS > multilib testing. > > OK to apply? OK. It would probably make sense to add at least one mips16 and one microMIPS configuration to build-many-glibcs.py so build failures for such configurations are more readily detected (though I suppose a wrong relocation like this might not result in a build failure?).
On Wed, 23 Nov 2016, Joseph Myers wrote: > > OK to apply? > > OK. Applied, thanks. > It would probably make sense to add at least one mips16 and one microMIPS > configuration to build-many-glibcs.py so build failures for such > configurations are more readily detected (though I suppose a wrong > relocation like this might not result in a build failure?). In the R_MIPS_JALR case BFD linker code checks the opcode of the instruction at the relocation location so that JALR and JR (for tail calls) are substituted with BAL and J respectively, and the microMIPS encodings are different, so no match happens and an invalid relocation is silently ignored. So no build failure will ever happen indeed. The R_MICROMIPS_JALR case is more complicated and currently not handled by the BFD linker at all, with the relocation always silently ignored, though I plan to get to it sometime. Most transformations are limited by the assymetry of the 16-bit instruction set, however some can still be made, e.g. JR16 can be changed into B16, and all can still be made in the `-minsn32' mode (which is however hardly ever used). This is probably the reason why it hasn't been implemented with the original microMIPS effort. I have no idea what GOLD does with these relocations, although I suppose any handling will have been semantically copied from the BFD linker. Maciej
Index: glibc/sysdeps/mips/mips32/crti.S =================================================================== --- glibc.orig/sysdeps/mips/mips32/crti.S 2016-11-17 15:28:32.000000000 +0000 +++ glibc/sysdeps/mips/mips32/crti.S 2016-11-17 15:36:52.838901381 +0000 @@ -40,6 +40,12 @@ #include <libc-symbols.h> +#ifdef __mips_micromips +# define JALR_RELOC R_MICROMIPS_JALR +#else +# define JALR_RELOC R_MIPS_JALR +#endif + #ifndef PREINIT_FUNCTION # define PREINIT_FUNCTION __gmon_start__ #endif @@ -71,13 +77,13 @@ lw $2,%got(PREINIT_FUNCTION)($28) beq $2,$0,.Lno_weak_fn lw $25,%call16(PREINIT_FUNCTION)($28) - .reloc 1f,R_MIPS_JALR,PREINIT_FUNCTION + .reloc 1f,JALR_RELOC,PREINIT_FUNCTION 1: jalr $25 .Lno_weak_fn: .insn #else lw $25,%got(PREINIT_FUNCTION)($28) - .reloc 1f,R_MIPS_JALR,PREINIT_FUNCTION + .reloc 1f,JALR_RELOC,PREINIT_FUNCTION 1: jalr $25 #endif Index: glibc/sysdeps/mips/mips64/n32/crti.S =================================================================== --- glibc.orig/sysdeps/mips/mips64/n32/crti.S 2016-11-17 15:30:48.000000000 +0000 +++ glibc/sysdeps/mips/mips64/n32/crti.S 2016-11-17 15:37:17.195020438 +0000 @@ -40,6 +40,12 @@ #include <libc-symbols.h> +#ifdef __mips_micromips +# define JALR_RELOC R_MICROMIPS_JALR +#else +# define JALR_RELOC R_MIPS_JALR +#endif + #ifndef PREINIT_FUNCTION # define PREINIT_FUNCTION __gmon_start__ #endif @@ -71,13 +77,13 @@ lw $2,%got_disp(PREINIT_FUNCTION)($28) beq $2,$0,.Lno_weak_fn lw $25,%call16(PREINIT_FUNCTION)($28) - .reloc 1f,R_MIPS_JALR,PREINIT_FUNCTION + .reloc 1f,JALR_RELOC,PREINIT_FUNCTION 1: jalr $25 .Lno_weak_fn: .insn #else lw $25,%got_disp(PREINIT_FUNCTION)($28) - .reloc 1f,R_MIPS_JALR,PREINIT_FUNCTION + .reloc 1f,JALR_RELOC,PREINIT_FUNCTION 1: jalr $25 #endif Index: glibc/sysdeps/mips/mips64/n64/crti.S =================================================================== --- glibc.orig/sysdeps/mips/mips64/n64/crti.S 2016-11-17 15:30:56.000000000 +0000 +++ glibc/sysdeps/mips/mips64/n64/crti.S 2016-11-17 15:38:09.690102763 +0000 @@ -40,6 +40,12 @@ #include <libc-symbols.h> +#ifdef __mips_micromips +# define JALR_RELOC R_MICROMIPS_JALR +#else +# define JALR_RELOC R_MIPS_JALR +#endif + #ifndef PREINIT_FUNCTION # define PREINIT_FUNCTION __gmon_start__ #endif @@ -71,13 +77,13 @@ ld $2,%got_disp(PREINIT_FUNCTION)($28) beq $2,$0,.Lno_weak_fn ld $25,%call16(PREINIT_FUNCTION)($28) - .reloc 1f,R_MIPS_JALR,PREINIT_FUNCTION + .reloc 1f,JALR_RELOC,PREINIT_FUNCTION 1: jalr $25 .Lno_weak_fn: .insn #else ld $25,%got_disp(PREINIT_FUNCTION)($28) - .reloc 1f,R_MIPS_JALR,PREINIT_FUNCTION + .reloc 1f,JALR_RELOC,PREINIT_FUNCTION 1: jalr $25 #endif