[PATCH] MIPS: use FR=1 for FPXX binary

From: YunQiang Su <yunqiang.su@cipunited.com>
To: tsbogend@alpha.franken.de, linux-mips@vger.kernel.org,
	jiaxun.yang@flygoat.com
Cc: stable@vger.kernel.org, YunQiang Su <yunqiang.su@cipunited.com>
Subject: [PATCH] MIPS: use FR=1 for FPXX binary
Date: Sat, 20 Feb 2021 06:16:35 +0000	[thread overview]
Message-ID: <20210220061635.9976-1-yunqiang.su@cipunited.com> (raw)

some binary, for example the output of golang, may be mark as FPXX,
while in fact they are still FP32.

Since FPXX binary can work with both FR=1 and FR=0, we force it to
use FR=1 here.

https://go-review.googlesource.com/c/go/+/239217
https://go-review.googlesource.com/c/go/+/237058
---
 arch/mips/kernel/elf.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/mips/kernel/elf.c b/arch/mips/kernel/elf.c
index 7b045d2a0b51..bf798ce0ec0e 100644
--- a/arch/mips/kernel/elf.c
+++ b/arch/mips/kernel/elf.c
@@ -234,9 +234,10 @@ int arch_check_elf(void *_ehdr, bool has_interpreter, void *_interp_ehdr,
 	 *   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
+	 *   handle both FR=1 and FR=0. Here, we use FR=0, because some
+	 *   binaries may be mark as FPXX by mistake (ie, output of golang).
+	 * - 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 +249,9 @@ 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 = 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

