[PATCH v2 07/21] target/i386: allow access_ptr to force slow path on failed probe

[Alex Bennée]

When we are using TCG plugin memory callbacks probe_access_internal
will return TLB_MMIO to force the slow path for memory access. This
results in probe_access returning NULL but the x86 access_ptr function
happily accepts an empty haddr resulting in segfault hilarity.

Check for an empty haddr to prevent the segfault and enable plugins to
track all the memory operations for the x86 save/restore helpers. As
we also want to run the slow path when instrumenting *-user we should
also not have the short cutting test_ptr macro.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2489
Fixes: 6d03226b42 (plugins: force slow path when plugins instrument memory ops)
Reviewed-by: Alexandre Iooss <erdnaxe@crans.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240807160236.2478459-1-alex.bennee@linaro.org>

---
v2
  - add comment around haddr1 test
  - drop test_ptr macro
---
 target/i386/tcg/access.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/target/i386/tcg/access.c b/target/i386/tcg/access.c
index 56a1181ea5..e68b73a24b 100644
--- a/target/i386/tcg/access.c
+++ b/target/i386/tcg/access.c
@@ -58,6 +58,11 @@ static void *access_ptr(X86Access *ac, vaddr addr, unsigned 
len)
 
     assert(addr >= ac->vaddr);
 
+    /* No haddr means probe_access wants to force slow path */
+    if (!ac->haddr1) {
+        return NULL;
+    }
+
 #ifdef CONFIG_USER_ONLY
     assert(offset <= ac->size1 - len);
     return ac->haddr1 + offset;
@@ -78,17 +83,11 @@ static void *access_ptr(X86Access *ac, vaddr addr, unsigned 
len)
 #endif
 }
 
-#ifdef CONFIG_USER_ONLY
-# define test_ptr(p)  true
-#else
-# define test_ptr(p)  likely(p)
-#endif
-
 uint8_t access_ldb(X86Access *ac, vaddr addr)
 {
     void *p = access_ptr(ac, addr, sizeof(uint8_t));
 
-    if (test_ptr(p)) {
+    if (likely(p)) {
         return ldub_p(p);
     }
     return cpu_ldub_mmuidx_ra(ac->env, addr, ac->mmu_idx, ac->ra);
@@ -98,7 +97,7 @@ uint16_t access_ldw(X86Access *ac, vaddr addr)
 {
     void *p = access_ptr(ac, addr, sizeof(uint16_t));
 
-    if (test_ptr(p)) {
+    if (likely(p)) {
         return lduw_le_p(p);
     }
     return cpu_lduw_le_mmuidx_ra(ac->env, addr, ac->mmu_idx, ac->ra);
@@ -108,7 +107,7 @@ uint32_t access_ldl(X86Access *ac, vaddr addr)
 {
     void *p = access_ptr(ac, addr, sizeof(uint32_t));
 
-    if (test_ptr(p)) {
+    if (likely(p)) {
         return ldl_le_p(p);
     }
     return cpu_ldl_le_mmuidx_ra(ac->env, addr, ac->mmu_idx, ac->ra);
@@ -118,7 +117,7 @@ uint64_t access_ldq(X86Access *ac, vaddr addr)
 {
     void *p = access_ptr(ac, addr, sizeof(uint64_t));
 
-    if (test_ptr(p)) {
+    if (likely(p)) {
         return ldq_le_p(p);
     }
     return cpu_ldq_le_mmuidx_ra(ac->env, addr, ac->mmu_idx, ac->ra);
@@ -128,7 +127,7 @@ void access_stb(X86Access *ac, vaddr addr, uint8_t val)
 {
     void *p = access_ptr(ac, addr, sizeof(uint8_t));
 
-    if (test_ptr(p)) {
+    if (likely(p)) {
         stb_p(p, val);
     } else {
         cpu_stb_mmuidx_ra(ac->env, addr, val, ac->mmu_idx, ac->ra);
@@ -139,7 +138,7 @@ void access_stw(X86Access *ac, vaddr addr, uint16_t val)
 {
     void *p = access_ptr(ac, addr, sizeof(uint16_t));
 
-    if (test_ptr(p)) {
+    if (likely(p)) {
         stw_le_p(p, val);
     } else {
         cpu_stw_le_mmuidx_ra(ac->env, addr, val, ac->mmu_idx, ac->ra);
@@ -150,7 +149,7 @@ void access_stl(X86Access *ac, vaddr addr, uint32_t val)
 {
     void *p = access_ptr(ac, addr, sizeof(uint32_t));
 
-    if (test_ptr(p)) {
+    if (likely(p)) {
         stl_le_p(p, val);
     } else {
         cpu_stl_le_mmuidx_ra(ac->env, addr, val, ac->mmu_idx, ac->ra);
@@ -161,7 +160,7 @@ void access_stq(X86Access *ac, vaddr addr, uint64_t val)
 {
     void *p = access_ptr(ac, addr, sizeof(uint64_t));
 
-    if (test_ptr(p)) {
+    if (likely(p)) {
         stq_le_p(p, val);
     } else {
         cpu_stq_le_mmuidx_ra(ac->env, addr, val, ac->mmu_idx, ac->ra);
-- 
2.39.2