[PATCH v2] linux-user/elfload: Implement ELF_HWCAP for RISC-V

[PATCH v2] linux-user/elfload: Implement ELF_HWCAP for RISC-V

[Kito Cheng]

Set I, M, A, F, D and C bit for hwcap if misa is set.

V2 Changes:
- Only set imafdc bits, sync with upstream linux kernel.

Signed-off-by: Kito Cheng <kito.cheng@sifive.com>
---
 linux-user/elfload.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 598ab8aa13..3cdc7d06e1 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1426,7 +1426,7 @@ static void elf_core_copy_regs(target_elf_gregset_t *regs,
 #ifdef TARGET_RISCV
 
 #define ELF_START_MMAP 0x80000000
-#define ELF_ARCH  EM_RISCV
+#define ELF_ARCH EM_RISCV
 
 #ifdef TARGET_RISCV32
 #define ELF_CLASS ELFCLASS32
@@ -1434,6 +1434,34 @@ static void elf_core_copy_regs(target_elf_gregset_t *regs,
 #define ELF_CLASS ELFCLASS64
 #endif
 
+#define ELF_HWCAP get_elf_hwcap()
+
+static uint32_t get_elf_hwcap(void)
+{
+    RISCVCPU *cpu = RISCV_CPU(thread_cpu);
+    uint32_t hwcap = 0;
+
+#define MISA_BIT(EXT) (1 << (EXT - 'A'))
+#define GET_EXT(EXT)				\
+    do {					\
+        if (cpu->env.misa & MISA_BIT(EXT)) {	\
+            hwcap |= MISA_BIT(EXT);		\
+        }					\
+    } while (0)
+
+    GET_EXT('I');
+    GET_EXT('M');
+    GET_EXT('A');
+    GET_EXT('F');
+    GET_EXT('D');
+    GET_EXT('C');
+
+#undef MISA_BIT
+#undef GET_EXT
+
+    return hwcap;
+}
+
 static inline void init_thread(struct target_pt_regs *regs,
                                struct image_info *infop)
 {
-- 
2.31.1

Re: [PATCH v2] linux-user/elfload: Implement ELF_HWCAP for RISC-V

[Richard Henderson]

On 7/4/21 11:43 PM, Kito Cheng wrote:
> +static uint32_t get_elf_hwcap(void)
> +{
> +    RISCVCPU *cpu = RISCV_CPU(thread_cpu);
> +    uint32_t hwcap = 0;
> +
> +#define MISA_BIT(EXT) (1 << (EXT - 'A'))
> +#define GET_EXT(EXT)				\
> +    do {					\
> +        if (cpu->env.misa & MISA_BIT(EXT)) {	\
> +            hwcap |= MISA_BIT(EXT);		\
> +        }					\
> +    } while (0)
> +
> +    GET_EXT('I');
> +    GET_EXT('M');
> +    GET_EXT('A');
> +    GET_EXT('F');
> +    GET_EXT('D');
> +    GET_EXT('C');

You're not transforming the bits; there's no reason to be so around-the-bush about this. 
Just use

     uint32_t mask = MISA_BIT('I') | ...
     return cpu->env.misa & mask;


r~