From 21bf9b06cb6d07c6cc437dfd47b47b28c2bb79db Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Fri, 17 Jan 2020 14:09:30 +0000 Subject: [PATCH] target/arm/arm-semi: fix SYS_OPEN to return nonzero filehandle According to the specification "Semihosting for AArch32 and Aarch64", the SYS_OPEN operation should return: - A nonzero handle if the call is successful - -1 if the call is not successful So, it should never return 0. Prior to commit 35e9a0a8ce4b ("target/arm/arm-semi: Make semihosting code hand out its own file descriptors"), the guest fd matched to the host fd. It returned a nonzero handle on success since the fd 0 is already used for stdin. Now that the guest fd is the index of guestfd_array, it starts from 0. I noticed this issue particularly because Trusted Firmware-A built with PLAT=qemu is no longer working. Its io_semihosting driver only handles a positive return value as a valid filehandle. Basically, there are two ways to fix this: - Use (guestfd - 1) as the index of guestfs_arrary. We need to insert increment/decrement to convert the guestfd and the array index back and forth. - Keep using guestfd as the index of guestfs_array. The first entry of guestfs_array is left unused. I thought the latter is simpler. We end up with wasting a small piece of memory for the unused first entry of guestfd_array, but this is probably not a big deal. Fixes: 35e9a0a8ce4b ("target/arm/arm-semi: Make semihosting code hand out its own file descriptors") Cc: qemu-stable@nongnu.org Signed-off-by: Masahiro Yamada Reviewed-by: Richard Henderson Message-id: 20200109041228.10131-1-masahiroy@kernel.org Signed-off-by: Peter Maydell --- target/arm/arm-semi.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/target/arm/arm-semi.c b/target/arm/arm-semi.c index 47d61f6fe1..788fe61b51 100644 --- a/target/arm/arm-semi.c +++ b/target/arm/arm-semi.c @@ -144,7 +144,8 @@ static int alloc_guestfd(void) guestfd_array = g_array_new(FALSE, TRUE, sizeof(GuestFD)); } - for (i = 0; i < guestfd_array->len; i++) { + /* SYS_OPEN should return nonzero handle on success. Start guestfd from 1 */ + for (i = 1; i < guestfd_array->len; i++) { GuestFD *gf = &g_array_index(guestfd_array, GuestFD, i); if (gf->type == GuestFDUnused) { @@ -168,7 +169,7 @@ static GuestFD *do_get_guestfd(int guestfd) return NULL; } - if (guestfd < 0 || guestfd >= guestfd_array->len) { + if (guestfd <= 0 || guestfd >= guestfd_array->len) { return NULL; } -- GitLab