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authorMaciej W. Rozycki <macro@mips.com>2018-05-25 12:37:45 +0100
committerMaciej W. Rozycki <macro@mips.com>2018-05-25 12:37:45 +0100
commitd8dab6c3bbe6432ff20237e621f2f3a3d30d4d4b (patch)
treeb0ed461248f6415f6d719151730705cec70cf016 /gdb/mips-linux-nat.c
parent3c69da406c72423afa4bd0e4fc4c805ec0b944a1 (diff)
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MIPS/Linux: Correct o32 core file FGR interpretation
Our interpretation of the layout of floating-point general registers (FGRs) in o32 MIPS/Linux core files is different from how the kernel makes them, affecting the CP0 Status.FR=0 aka FP32 mode (we don't currently support the CP0 Status.FR=1 aka FP64 mode with the o32 ABI). In the FP32 mode pairs of consecutive even/odd-numbered 32-bit registers are placed together as 64-bit values in even-indexed 64-bit slots corresponding to the even index, leaving the odd-indexed 64-bit slots unused. These 64-bit values are stored according to the endianness in effect, which is how the MIPS II SDC1 instruction would store them. It has always been like that with the Linux kernel for MIPS II and higher ISA processors, which are the vast majority ever supported, as it is indeed SDC1 that the kernel uses to store FGRs in a floating-point context. With MIPS I processors, which lack the SDC1 instruction, a layout that we expect used to be used long ago, but it was corrected for consistency with newer processors back in 2002, with `linux-mips.org' (LMO) commit 42533948caac ("Major pile of FP emulator changes."), the fix corrected with LMO commit 849fa7a50dff ("R3k FPU ptrace() handling fixes."), and then broken and fixed over and over again, until last time fixed with commit 80cbfad79096 ("MIPS: Correct MIPS I FP context layout"). Consequently the values we see in FP32 core files or produce with the `gcore' command are different from those obtained from the same FP context of a live process, e.g. with a big-endian configuration these live values: (gdb) info registers float f0: 0x4b5c6d7e flt: 14445950 dbl: 1.7446153562345001e-274 f1: 0x0718293a flt: 1.14473244e-34 f2: 0xc3d4e5f6 flt: -425.79657 dbl: -1.046160437414959e-233 f3: 0x8f90a1b2 flt: -1.42617791e-29 f4: 0x4c5d6e7f flt: 58046972 dbl: 1.1908587841220294e-269 f5: 0x08192a3b flt: 4.60914044e-34 f6: 0xc4d5e6f7 flt: -1711.21765 dbl: -6.2784661835068965e-306 f7: 0x8091a2b3 flt: -1.33745124e-38 f8: 0x45566778 flt: 3430.4668 dbl: 1.6530355595710607e-303 f9: 0x01122334 flt: 2.68412219e-38 f10: 0xcddeeff0 flt: -467533312 dbl: -2.1174864564135575e-262 f11: 0x899aabbc flt: -3.72356497e-33 f12: 0x46576879 flt: 13786.1182 dbl: 1.143296486773654e-298 f13: 0x02132435 flt: 1.08102453e-37 f14: 0xcedfe0f1 flt: -1.87803046e+09 dbl: -1.4399511533369862e-257 f15: 0x8a9bacbd flt: -1.4990934e-32 f16: 0x4758697a flt: 55401.4766 dbl: 7.8856820439568725e-294 f17: 0x03142536 flt: 4.3536007e-37 f18: 0xcfd0e1f2 flt: -7.00893696e+09 dbl: -9.7791926757340559e-253 f19: 0x8b9cadbe flt: -6.03504325e-32 f20: 0x48596a7b flt: 222633.922 dbl: 5.4255001483306113e-289 f21: 0x04152637 flt: 1.75324132e-36 f22: 0xc0d1e2f3 flt: -6.55895376 dbl: -6.6332401002310683e-248 f23: 0x8c9daebf flt: -2.42948516e-31 f24: 0x495a6b7c flt: 894647.75 dbl: 3.7244369058749787e-284 f25: 0x05162738 flt: 7.06016945e-36 f26: 0xc1d2e3f4 flt: -26.3613052 dbl: -4.4941535759306202e-243 f27: 0x8d9eafb0 flt: -9.77979703e-31 f28: 0x4a5b6c7d flt: 3595039.25 dbl: 2.5514593711161396e-279 f29: 0x06172839 flt: 2.84294945e-35 f30: 0xc2d3e4f5 flt: -105.947182 dbl: -3.035646690850097e-238 f31: 0x8e9fa0b1 flt: -3.93512664e-30 fcsr: 0x0 fir: 0xf30000 (gdb) show up in a core file as these: (gdb) info registers float f0: 0x0718293a flt: 1.14473244e-34 dbl: nan f1: 0x7ff80000 flt: nan f2: 0x8f90a1b2 flt: -1.42617791e-29 dbl: nan f3: 0x7ff80000 flt: nan f4: 0x08192a3b flt: 4.60914044e-34 dbl: nan f5: 0x7ff80000 flt: nan f6: 0x8091a2b3 flt: -1.33745124e-38 dbl: nan f7: 0x7ff80000 flt: nan f8: 0x01122334 flt: 2.68412219e-38 dbl: nan f9: 0x7ff80000 flt: nan f10: 0x899aabbc flt: -3.72356497e-33 dbl: nan f11: 0x7ff80000 flt: nan f12: 0x02132435 flt: 1.08102453e-37 dbl: nan f13: 0x7ff80000 flt: nan f14: 0x8a9bacbd flt: -1.4990934e-32 dbl: nan f15: 0x7ff80000 flt: nan f16: 0x03142536 flt: 4.3536007e-37 dbl: nan f17: 0x7ff80000 flt: nan f18: 0x8b9cadbe flt: -6.03504325e-32 dbl: nan f19: 0x7ff80000 flt: nan f20: 0x04152637 flt: 1.75324132e-36 dbl: nan f21: 0x7ff80000 flt: nan f22: 0x8c9daebf flt: -2.42948516e-31 dbl: nan f23: 0x7ff80000 flt: nan f24: 0x05162738 flt: 7.06016945e-36 dbl: nan f25: 0x7ff80000 flt: nan f26: 0x8d9eafb0 flt: -9.77979703e-31 dbl: nan f27: 0x7ff80000 flt: nan f28: 0x06172839 flt: 2.84294945e-35 dbl: nan f29: 0x7ff80000 flt: nan f30: 0x8e9fa0b1 flt: -3.93512664e-30 dbl: nan f31: 0x7ff80000 flt: nan (gdb) Notice how values from odd-numbered registers are shown in corresponding even-numbered registers and how dummy 0x7ff80000 NaN values, which the kernel places in unused slots, are reported in odd-numbered registers. Correct our intepretation then, to match the kernel's. As it happens the o32 FGR core file representation matches that used by the `ptrace' PTRACE_GETFPREGS request, which means our 64-bit handlers can be readily used, as they already correctly handle the differences between o32 FP32 mode vs n32/n64 representations. Adjust comments accordingly throughout, in particular remove a reference to the r3000/tx39 MIPS I processor peculiarity, long irrelevant. Add a test case to verify correctness. Avoid GCC bugs and limitations in the test case where possible; the test case still fails to build with GCC 8 and the o32 FP64 mode (i.e. with `-mips32r2 -mfp64' options) giving: mips-fpregset-core.c: In function 'main': mips-fpregset-core.c:66:3: error: inconsistent operand constraints in an 'asm' asm ( ^~~ (GCC PR target/85909), but that is not a concern for us as yet, because as noted above we do not currently support the o32 FP64 mode anyway. gdb/ * mips-linux-tdep.h (mips_supply_fpregset, mips_fill_fpregset): Remove prototypes. * mips-linux-nat.c (supply_fpregset): Always call `mips64_supply_fpregset' rather than `mips_supply_fpregset'. (fill_fpregset): Always call `mips64_fill_fpregset' rather than `mips_fill_fpregset'. * mips-linux-tdep.c (mips_supply_fpregset) (mips_supply_fpregset_wrapper, mips_fill_fpregset) (mips_fill_fpregset_wrapper): Remove functions. (mips64_supply_fpregset, mips64_fill_fpregset): Update comments. (mips_linux_fpregset): Remove variable. (mips_linux_iterate_over_regset_sections): Use `mips64_linux_fpregset' in place of `mips_linux_fpregset'. (mips_linux_o32_sigframe_init): Remove comment. gdb/testsuite/ * gdb.arch/mips-fpregset-core.exp: New test. * gdb.arch/mips-fpregset-core.c: New test source.
Diffstat (limited to 'gdb/mips-linux-nat.c')
-rw-r--r--gdb/mips-linux-nat.c12
1 files changed, 2 insertions, 10 deletions
diff --git a/gdb/mips-linux-nat.c b/gdb/mips-linux-nat.c
index a9f0b79..3683107 100644
--- a/gdb/mips-linux-nat.c
+++ b/gdb/mips-linux-nat.c
@@ -224,22 +224,14 @@ fill_gregset (const struct regcache *regcache,
void
supply_fpregset (struct regcache *regcache, const gdb_fpregset_t *fpregsetp)
{
- if (mips_isa_regsize (regcache->arch ()) == 4)
- mips_supply_fpregset (regcache, (const mips_elf_fpregset_t *) fpregsetp);
- else
- mips64_supply_fpregset (regcache,
- (const mips64_elf_fpregset_t *) fpregsetp);
+ mips64_supply_fpregset (regcache, (const mips64_elf_fpregset_t *) fpregsetp);
}
void
fill_fpregset (const struct regcache *regcache,
gdb_fpregset_t *fpregsetp, int regno)
{
- if (mips_isa_regsize (regcache->arch ()) == 4)
- mips_fill_fpregset (regcache, (mips_elf_fpregset_t *) fpregsetp, regno);
- else
- mips64_fill_fpregset (regcache,
- (mips64_elf_fpregset_t *) fpregsetp, regno);
+ mips64_fill_fpregset (regcache, (mips64_elf_fpregset_t *) fpregsetp, regno);
}