MIPS: Kconfig option to better exercise/debug hybrid FPRs

The hybrid FPR scheme exists to allow for compatibility between existing
FP32 code and newly compiled FP64A code. Such code should hopefully be
rare in the real world, and for the moment is difficult to come across.
All code except that built for the FP64 ABI can correctly execute using
the hybrid FPR scheme, so debugging the hybrid FPR implementation can
be eased by forcing all such code to use it. This is undesirable in
general due to the trap & emulate overhead of the hybrid FPR
implementation, but is a very useful option to have for debugging.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7680/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/mips/kernel/elf.c b/arch/mips/kernel/elf.c
index 0933e0726f64..c92b15df6893 100644
--- a/arch/mips/kernel/elf.c
+++ b/arch/mips/kernel/elf.c
@@ -134,6 +134,24 @@ int arch_check_elf(void *_ehdr, bool has_interpreter,
 
 void mips_set_personality_fp(struct arch_elf_state *state)
 {
+        if (config_enabled(CONFIG_FP32XX_HYBRID_FPRS)) {
+                /*
+                 * Use hybrid FPRs for all code which can correctly execute
+                 * with that mode.
+                 */
+                switch (state->overall_abi) {
+                case MIPS_ABI_FP_DOUBLE:
+                case MIPS_ABI_FP_SINGLE:
+                case MIPS_ABI_FP_SOFT:
+                case MIPS_ABI_FP_XX:
+                case MIPS_ABI_FP_ANY:
+                        /* FR=1, FRE=1 */
+                        clear_thread_flag(TIF_32BIT_FPREGS);
+                        set_thread_flag(TIF_HYBRID_FPREGS);
+                        return;
+                }
+        }
+
         switch (state->overall_abi) {
         case MIPS_ABI_FP_DOUBLE:
         case MIPS_ABI_FP_SINGLE: