On Thu, Mar 4, 2021 at 11:06 AM YunQiang Su <syq@xxxxxxxxxx> wrote: > > From: YunQiang Su <yunqiang.su@xxxxxxxxxxxxx> > > The MIPS FPU may have 3 mode: > FR=0: MIPS I style, all of the FPR are single. > FR=1: all 32 FPR can be double. > FRE: redirecting the rw of odd-FPR to the upper 32bit of even-double FPR. > > The binary may have 3 mode: > FP32: can only work with FR=0 and FRE mode > FPXX: can work with all of FR=0/FR=1/FRE mode. > FP64: can only work with FR=1 mode > > Some binary, for example the output of golang, may be mark as FPXX, > while in fact they are FP32. It is caused by the bug of design and linker: > Object produced by pure Go has no FP annotation while in fact they are FP32; > if we link them with the C module which marked as FPXX, > the result will be marked as FPXX. If these fake-FPXX binaries is executed > in FR=1 mode, some problem will happen. > > In Golang, now we add the FP32 annotation, so the future golang programs > won't have this problem. While for the existing binaries, we need a > kernel workaround. > > Currently, FR=1 mode is used for all FPXX binary, it makes some wrong > behivour of the binaries. Since FPXX binary can work with both FR=1 and FR=0, > we force it to use FR=0 or FRE (for R6 CPU). > > Reference: > > https://web.archive.org/web/20180828210612/https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking > > https://go-review.googlesource.com/c/go/+/239217 > https://go-review.googlesource.com/c/go/+/237058 > > Signed-off-by: YunQiang Su <yunqiang.su@xxxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # 4.19+ Here goes the '---' git separator: --- To remove the following notes when applying, not really useful in the git history. > > v6->v7: > Use FRE mode for pre-R6 binaries on R6 CPU. > > v5->v6: > Rollback to V3, aka remove config option. > > v4->v5: > Fix CONFIG_MIPS_O32_FPXX_USE_FR0 usage: if -> ifdef > > v3->v4: > introduce a config option: CONFIG_MIPS_O32_FPXX_USE_FR0 > > v2->v3: > commit message: add Signed-off-by and Cc to stable. > > v1->v2: > Fix bad commit message: in fact, we are switching to FR=0 > --- > arch/mips/kernel/elf.c | 20 +++++++++++++------- > 1 file changed, 13 insertions(+), 7 deletions(-) > > diff --git a/arch/mips/kernel/elf.c b/arch/mips/kernel/elf.c > index 7b045d2a0b51..4d4db619544b 100644 > --- a/arch/mips/kernel/elf.c > +++ b/arch/mips/kernel/elf.c > @@ -232,11 +232,16 @@ int arch_check_elf(void *_ehdr, bool has_interpreter, void *_interp_ehdr, > * that inherently require the hybrid FP mode. > * - If FR1 and FRDEFAULT is true, that means we hit the any-abi or > * fpxx case. This is because, in any-ABI (or no-ABI) we have no FPU > - * instructions so we don't care about the mode. We will simply use > - * the one preferred by the hardware. In fpxx case, that ABI can > - * handle both FR=1 and FR=0, so, again, we simply choose the one > - * preferred by the hardware. Next, if we only use single-precision > - * FPU instructions, and the default ABI FPU mode is not good > + * instructions so we don't care about the mode. > + * In fpxx case, that ABI can handle all of FR=1/FR=0/FRE mode. > + * Here, we need to use FR=0/FRE mode instead of FR=1, because some binaries > + * may be mark as FPXX by mistake due to bugs of design and linker: > + * The object produced by pure Go has no FP annotation, > + * then is treated as any-ABI by linker, although in fact they are FP32; > + * if any-ABI object is linked with FPXX object, the result will be mark as FPXX. > + * Then the problem happens: run FP32 binaries in FR=1 mode. > + * - If we only use single-precision FPU instructions, > + * and the default ABI FPU mode is not good > * (ie single + any ABI combination), we set again the FPU mode to the > * one is preferred by the hardware. Next, if we know that the code > * will only use single-precision instructions, shown by single being > @@ -248,8 +253,9 @@ int arch_check_elf(void *_ehdr, bool has_interpreter, void *_interp_ehdr, > */ > if (prog_req.fre && !prog_req.frdefault && !prog_req.fr1) > state->overall_fp_mode = FP_FRE; > - else if ((prog_req.fr1 && prog_req.frdefault) || > - (prog_req.single && !prog_req.frdefault)) > + else if (prog_req.fr1 && prog_req.frdefault) > + state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0; > + else if (prog_req.single && !prog_req.frdefault) > /* Make sure 64-bit MIPS III/IV/64R1 will not pick FR1 */ > state->overall_fp_mode = ((raw_current_cpu_data.fpu_id & MIPS_FPIR_F64) && > cpu_has_mips_r2_r6) ? > -- > 2.20.1 >
