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@@ -0,0 +1,78 @@
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+From 318f83f387678a3c0a2a729b506613011c6830b2 Mon Sep 17 00:00:00 2001
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+From: Masahiro Yamada <masahiroy@kernel.org>
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+Date: Fri, 17 Jan 2020 14:09:30 +0000
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+Subject: [PATCH] target/arm/arm-semi: fix SYS_OPEN to return nonzero
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+ filehandle
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+
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+According to the specification "Semihosting for AArch32 and Aarch64",
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+the SYS_OPEN operation should return:
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+
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+ - A nonzero handle if the call is successful
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+ - -1 if the call is not successful
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+
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+So, it should never return 0.
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+
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+Prior to commit 35e9a0a8ce4b ("target/arm/arm-semi: Make semihosting
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+code hand out its own file descriptors"), the guest fd matched to the
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+host fd. It returned a nonzero handle on success since the fd 0 is
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+already used for stdin.
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+
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+Now that the guest fd is the index of guestfd_array, it starts from 0.
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+
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+I noticed this issue particularly because Trusted Firmware-A built with
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+PLAT=qemu is no longer working. Its io_semihosting driver only handles
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+a positive return value as a valid filehandle.
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+
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+Basically, there are two ways to fix this:
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+
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+ - Use (guestfd - 1) as the index of guestfs_arrary. We need to insert
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+ increment/decrement to convert the guestfd and the array index back
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+ and forth.
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+
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+ - Keep using guestfd as the index of guestfs_array. The first entry
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+ of guestfs_array is left unused.
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+
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+I thought the latter is simpler. We end up with wasting a small piece
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+of memory for the unused first entry of guestfd_array, but this is
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+probably not a big deal.
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+
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+Fixes: 35e9a0a8ce4b ("target/arm/arm-semi: Make semihosting code hand out its own file descriptors")
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+Cc: qemu-stable@nongnu.org
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+Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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+Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
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+Message-id: 20200109041228.10131-1-masahiroy@kernel.org
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+Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
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+
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+(cherry picked from commit 21bf9b06cb6d07c6cc437dfd47b47b28c2bb79db)
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+Signed-off-by: Adrien Grassein <adrien.grassein@smile.fr>
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+Signed-off-by: Romain Naour <romain.naour@smile.fr>
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+---
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+ target/arm/arm-semi.c | 5 +++--
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+ 1 file changed, 3 insertions(+), 2 deletions(-)
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+
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+diff --git a/target/arm/arm-semi.c b/target/arm/arm-semi.c
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+index 6f7b6d801b..4275dfc345 100644
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+--- a/target/arm/arm-semi.c
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++++ b/target/arm/arm-semi.c
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+@@ -144,7 +144,8 @@ static int alloc_guestfd(void)
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+ guestfd_array = g_array_new(FALSE, TRUE, sizeof(GuestFD));
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+ }
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+
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+- for (i = 0; i < guestfd_array->len; i++) {
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++ /* SYS_OPEN should return nonzero handle on success. Start guestfd from 1 */
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++ for (i = 1; i < guestfd_array->len; i++) {
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+ GuestFD *gf = &g_array_index(guestfd_array, GuestFD, i);
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+
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+ if (gf->type == GuestFDUnused) {
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+@@ -168,7 +169,7 @@ static GuestFD *do_get_guestfd(int guestfd)
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+ return NULL;
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+ }
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+
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+- if (guestfd < 0 || guestfd >= guestfd_array->len) {
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++ if (guestfd <= 0 || guestfd >= guestfd_array->len) {
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+ return NULL;
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+ }
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+
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+--
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+2.24.1
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+
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Adrien Grassein