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Re: [Qemu-devel] [Qemu-arm] [PATCH 11/13] target/arm/arm-semi: Implement
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [Qemu-arm] [PATCH 11/13] target/arm/arm-semi: Implement support for semihosting feature detection |
Date: |
Thu, 12 Sep 2019 12:56:05 +0100 |
User-agent: |
mu4e 1.3.4; emacs 27.0.50 |
Peter Maydell <address@hidden> writes:
> Version 2.0 of the semihosting specification added support for
> allowing a guest to detect whether the implementation supported
> particular features. This works by the guest opening a magic
> file ":semihosting-features", which contains a fixed set of
> data with some magic numbers followed by a sequence of bytes
> with feature flags. The file is expected to behave sensibly
> for the various semihosting calls which operate on files
> (SYS_FLEN, SYS_SEEK, etc).
>
> Implement this as another kind of guest FD using our function
> table dispatch mechanism. Initially we report no extended
> features, so we have just one feature flag byte which is zero.
>
> Signed-off-by: Peter Maydell <address@hidden>
with your EACCESS suggestion:
Reviewed-by: Alex Bennée <address@hidden>
> ---
> target/arm/arm-semi.c | 107 +++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 106 insertions(+), 1 deletion(-)
>
> diff --git a/target/arm/arm-semi.c b/target/arm/arm-semi.c
> index f9019b00b8d..531084b7799 100644
> --- a/target/arm/arm-semi.c
> +++ b/target/arm/arm-semi.c
> @@ -117,6 +117,7 @@ typedef enum GuestFDType {
> GuestFDUnused = 0,
> GuestFDHost = 1,
> GuestFDGDB = 2,
> + GuestFDFeatureFile = 3,
> } GuestFDType;
>
> /*
> @@ -125,7 +126,10 @@ typedef enum GuestFDType {
> */
> typedef struct GuestFD {
> GuestFDType type;
> - int hostfd;
> + union {
> + int hostfd;
> + target_ulong featurefile_offset;
> + };
> } GuestFD;
>
> static GArray *guestfd_array;
> @@ -467,6 +471,87 @@ static uint32_t gdb_flenfn(TaskState *ts, ARMCPU *cpu,
> GuestFD *gf)
> gf->hostfd, arm_flen_buf(cpu));
> }
>
> +#define SHFB_MAGIC_0 0x53
> +#define SHFB_MAGIC_1 0x48
> +#define SHFB_MAGIC_2 0x46
> +#define SHFB_MAGIC_3 0x42
> +
> +static const uint8_t featurefile_data[] = {
> + SHFB_MAGIC_0,
> + SHFB_MAGIC_1,
> + SHFB_MAGIC_2,
> + SHFB_MAGIC_3,
> + 0, /* Feature byte 0 */
> +};
> +
> +static void init_featurefile_guestfd(int guestfd)
> +{
> + GuestFD *gf = do_get_guestfd(guestfd);
> +
> + assert(gf);
> + gf->type = GuestFDFeatureFile;
> + gf->featurefile_offset = 0;
> +}
> +
> +static uint32_t featurefile_closefn(TaskState *ts, ARMCPU *cpu, GuestFD *gf)
> +{
> + /* Nothing to do */
> + return 0;
> +}
> +
> +static uint32_t featurefile_writefn(TaskState *ts, ARMCPU *cpu, GuestFD *gf,
> + target_ulong buf, uint32_t len)
> +{
> + /* This fd can never be open for writing */
> + errno = EBADF;
> + return set_swi_errno(ts, -1);
> +}
> +
> +static uint32_t featurefile_readfn(TaskState *ts, ARMCPU *cpu, GuestFD *gf,
> + target_ulong buf, uint32_t len)
> +{
> + uint32_t i;
> +#ifndef CONFIG_USER_ONLY
> + CPUARMState *env = &cpu->env;
> +#endif
> + char *s;
> +
> + s = lock_user(VERIFY_WRITE, buf, len, 0);
> + if (!s) {
> + return len;
> + }
> +
> + for (i = 0; i < len; i++) {
> + if (gf->featurefile_offset >= sizeof(featurefile_data)) {
> + break;
> + }
> + s[i] = featurefile_data[gf->featurefile_offset];
> + gf->featurefile_offset++;
> + }
> +
> + unlock_user(s, buf, len);
> +
> + /* Return number of bytes not read */
> + return len - i;
> +}
> +
> +static uint32_t featurefile_isattyfn(TaskState *ts, ARMCPU *cpu, GuestFD *gf)
> +{
> + return 0;
> +}
> +
> +static uint32_t featurefile_seekfn(TaskState *ts, ARMCPU *cpu, GuestFD *gf,
> + target_ulong offset)
> +{
> + gf->featurefile_offset = offset;
> + return 0;
> +}
> +
> +static uint32_t featurefile_flenfn(TaskState *ts, ARMCPU *cpu, GuestFD *gf)
> +{
> + return sizeof(featurefile_data);
> +}
> +
> typedef struct GuestFDFunctions {
> sys_closefn *closefn;
> sys_writefn *writefn;
> @@ -493,6 +578,14 @@ static const GuestFDFunctions guestfd_fns[] = {
> .seekfn = gdb_seekfn,
> .flenfn = gdb_flenfn,
> },
> + [GuestFDFeatureFile] = {
> + .closefn = featurefile_closefn,
> + .writefn = featurefile_writefn,
> + .readfn = featurefile_readfn,
> + .isattyfn = featurefile_isattyfn,
> + .seekfn = featurefile_seekfn,
> + .flenfn = featurefile_flenfn,
> + },
> };
>
> /* Read the input value from the argument block; fail the semihosting
> @@ -586,6 +679,18 @@ target_ulong do_arm_semihosting(CPUARMState *env)
> unlock_user(s, arg0, 0);
> return guestfd;
> }
> + if (strcmp(s, ":semihosting-features") == 0) {
> + unlock_user(s, arg0, 0);
> + /* We must fail opens for modes other than 0 ('r') or 1 ('rb') */
> + if (arg1 != 0 && arg1 != 1) {
> + dealloc_guestfd(guestfd);
> + errno = EINVAL;
> + return set_swi_errno(ts, -1);
> + }
> + init_featurefile_guestfd(guestfd);
> + return guestfd;
> + }
> +
> if (use_gdb_syscalls()) {
> ret = arm_gdb_syscall(cpu, arm_semi_cb, "open,%s,%x,1a4", arg0,
> (int)arg2+1, gdb_open_modeflags[arg1]);
--
Alex Bennée
- Re: [Qemu-devel] [Qemu-arm] [PATCH 03/13] target/arm/arm-semi: Make semihosting code hand out its own file descriptors, (continued)