Re: [PATCH v3 3/5] linux-user/riscv: Add extended state to sigcontext

[Alistair Francis <alistair23@gmail.com>]

On Sun, Mar 22, 2026 at 12:16 AM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> Linux/riscv has extended the sigcontext with padding and an
> extended state structure that can save various optional
> features like vector in a flexible format. Update the
> linux-user signal handling to this new structure.
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  linux-user/riscv/signal.c         | 93 +++++++++++++++++++++++++++----
>  linux-user/riscv/vdso-asmoffset.h |  4 +-
>  2 files changed, 85 insertions(+), 12 deletions(-)
>
> diff --git a/linux-user/riscv/signal.c b/linux-user/riscv/signal.c
> index ece276f85f..e20b9ac177 100644
> --- a/linux-user/riscv/signal.c
> +++ b/linux-user/riscv/signal.c
> @@ -31,14 +31,43 @@
>
>     The code below is qemu re-implementation of arch/riscv/kernel/signal.c */
>
> -struct target_sigcontext {
> +struct target_gp_state {
>      abi_long pc;
>      abi_long gpr[31]; /* x0 is not present, so all offsets must be -1 */
> +};
> +
> +struct target_fp_state {
>      uint64_t fpr[32];
>      uint32_t fcsr;
> +};
> +
> +/* The Magic number for signal context frame header. */
> +#define END_MAGIC       0x0
> +
> +/* The size of END signal context header. */
> +#define END_HDR_SIZE    0x0
> +
> +struct target_ctx_hdr {
> +    uint32_t magic;
> +    uint32_t size;
> +};
> +
> +struct target_extra_ext_header {
> +    uint32_t __padding[129] __attribute__((aligned(16)));
> +    uint32_t reserved;
> +    struct target_ctx_hdr hdr;
> +};
> +
> +struct target_sigcontext {
> +    struct target_gp_state sc_regs;
> +    union {
> +        struct target_fp_state sc_fpregs;
> +        struct target_extra_ext_header sc_extdesc;
> +    };
>  }; /* cf. riscv-linux:arch/riscv/include/uapi/asm/ptrace.h */

I would argue that arch/riscv/include/uapi/asm/sigcontext.h is a
better pointer, but both work

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

>
> -QEMU_BUILD_BUG_ON(offsetof(struct target_sigcontext, fpr) != offsetof_freg0);
> +QEMU_BUILD_BUG_ON(offsetof(struct target_sigcontext, sc_fpregs.fpr) !=
> +                  offsetof_freg0);
>
>  struct target_ucontext {
>      abi_ulong uc_flags;
> @@ -79,19 +108,26 @@ static abi_ulong get_sigframe(struct target_sigaction *ka,
>
>  static void setup_sigcontext(struct target_sigcontext *sc, CPURISCVState *env)
>  {
> +    struct target_ctx_hdr *hdr;
>      int i;
>
> -    __put_user(env->pc, &sc->pc);
> +    __put_user(env->pc, &sc->sc_regs.pc);
>
>      for (i = 1; i < 32; i++) {
> -        __put_user(env->gpr[i], &sc->gpr[i - 1]);
> +        __put_user(env->gpr[i], &sc->sc_regs.gpr[i - 1]);
>      }
>      for (i = 0; i < 32; i++) {
> -        __put_user(env->fpr[i], &sc->fpr[i]);
> +        __put_user(env->fpr[i], &sc->sc_fpregs.fpr[i]);
>      }
>
>      uint32_t fcsr = riscv_csr_read(env, CSR_FCSR);
> -    __put_user(fcsr, &sc->fcsr);
> +    __put_user(fcsr, &sc->sc_fpregs.fcsr);
> +
> +    __put_user(0, &sc->sc_extdesc.reserved);
> +
> +    hdr = &sc->sc_extdesc.hdr;
> +    __put_user(END_MAGIC, &hdr->magic);
> +    __put_user(END_HDR_SIZE, &hdr->size);
>  }
>
>  static void setup_ucontext(struct target_ucontext *uc,
> @@ -147,21 +183,58 @@ badframe:
>
>  static bool restore_sigcontext(CPURISCVState *env, struct target_sigcontext *sc)
>  {
> +    struct target_ctx_hdr *hdr;
> +    uint32_t rsv, magic, size;
>      int i;
>
> -    __get_user(env->pc, &sc->pc);
> +    __get_user(env->pc, &sc->sc_regs.pc);
>
>      for (i = 1; i < 32; ++i) {
> -        __get_user(env->gpr[i], &sc->gpr[i - 1]);
> +        __get_user(env->gpr[i], &sc->sc_regs.gpr[i - 1]);
>      }
>      for (i = 0; i < 32; ++i) {
> -        __get_user(env->fpr[i], &sc->fpr[i]);
> +        __get_user(env->fpr[i], &sc->sc_fpregs.fpr[i]);
>      }
>
>      uint32_t fcsr;
> -    __get_user(fcsr, &sc->fcsr);
> +    __get_user(fcsr, &sc->sc_fpregs.fcsr);
>      riscv_csr_write(env, CSR_FCSR, fcsr);
>
> +    hdr = &sc->sc_extdesc.hdr;
> +    __get_user(rsv, &sc->sc_extdesc.reserved);
> +    if (rsv != 0) {
> +        qemu_log_mask(LOG_GUEST_ERROR, "signal: sigcontext reserved field is "
> +                                       "non-zero\n");
> +        return false;
> +    }
> +
> +    __get_user(magic, &hdr->magic);
> +    while (magic != END_MAGIC) {
> +        switch (magic) {
> +        default:
> +            qemu_log_mask(LOG_GUEST_ERROR, "signal: unknown extended state in "
> +                                           "sigcontext, magic=0x%08x\n", magic);
> +            return false;
> +        }
> +
> +        __get_user(size, &hdr->size);
> +        if (size == 0) {
> +            qemu_log_mask(LOG_GUEST_ERROR, "signal: extended state in "
> +                                           "sigcontext has size 0\n");
> +            return false;
> +        }
> +
> +        hdr = (void *)hdr + size;
> +        __get_user(magic, &hdr->magic);
> +    }
> +
> +    __get_user(size, &hdr->size);
> +    if (size != END_HDR_SIZE) {
> +        qemu_log_mask(LOG_GUEST_ERROR, "signal: extended state end header has "
> +                                       "size=%u (should be 0)\n", size);
> +        return false;
> +    }
> +
>      return true;
>  }
>
> diff --git a/linux-user/riscv/vdso-asmoffset.h b/linux-user/riscv/vdso-asmoffset.h
> index 123902ef61..92e8ac10ab 100644
> --- a/linux-user/riscv/vdso-asmoffset.h
> +++ b/linux-user/riscv/vdso-asmoffset.h
> @@ -1,9 +1,9 @@
>  #ifdef TARGET_ABI32
> -# define sizeof_rt_sigframe     0x2b0
> +# define sizeof_rt_sigframe     0x3b0
>  # define offsetof_uc_mcontext   0x120
>  # define offsetof_freg0         0x80
>  #else
> -# define sizeof_rt_sigframe     0x340
> +# define sizeof_rt_sigframe     0x440
>  # define offsetof_uc_mcontext   0x130
>  # define offsetof_freg0         0x100
>  #endif
> --
> 2.51.0
>
>