Fix recommitted pages not being zeroed when madvise is not available.

.github/workflows/build.yml

@@ -404,7 +404,7 @@ jobs:
           - arch: aarch64_cortex-a53-static
             openwrt: 'target=sunxi subtarget=cortexa53'
             target_cpu: arm64
-            extra: 'arm_cpu="cortex-a53" build_static=true'
+            extra: 'arm_cpu="cortex-a53" build_static=true no_madvise_syscall=true'
           - arch: aarch64_cortex-a72
             openwrt: 'target=mvebu subtarget=cortexa72'
             target_cpu: arm64
@@ -443,7 +443,7 @@ jobs:
           - arch: arm_cortex-a7_neon-vfpv4-static
             openwrt: 'target=sunxi subtarget=cortexa7'
             target_cpu: arm
-            extra: 'arm_version=0 arm_cpu="cortex-a7" arm_fpu="neon-vfpv4" arm_float_abi="hard" arm_use_neon=true build_static=true'
+            extra: 'arm_version=0 arm_cpu="cortex-a7" arm_fpu="neon-vfpv4" arm_float_abi="hard" arm_use_neon=true build_static=true no_madvise_syscall=true'
           - arch: arm_cortex-a8_vfpv3
             openwrt: 'target=sunxi subtarget=cortexa8'
             target_cpu: arm
@@ -455,7 +455,7 @@ jobs:
           - arch: arm_cortex-a9-static
             openwrt: 'target=bcm53xx subtarget=generic'
             target_cpu: arm
-            extra: 'arm_version=0 arm_cpu="cortex-a9" arm_float_abi="soft" arm_use_neon=false build_static=true'
+            extra: 'arm_version=0 arm_cpu="cortex-a9" arm_float_abi="soft" arm_use_neon=false build_static=true no_madvise_syscall=true'
           - arch: arm_cortex-a9_neon
             openwrt: 'target=zynq subtarget=generic'
             target_cpu: arm
@@ -479,7 +479,7 @@ jobs:
           - arch: mipsel_24kc-static
             openwrt: 'target=ramips subtarget=rt305x'
             target_cpu: mipsel
-            extra: 'mips_arch_variant="r2" mips_float_abi="soft" build_static=true'
+            extra: 'mips_arch_variant="r2" mips_float_abi="soft" build_static=true no_madvise_syscall=true'
           - arch: mipsel_mips32
             openwrt: 'target=bcm47xx subtarget=generic'
             target_cpu: mipsel

src/base/allocator/partition_allocator/page_allocator.h

@@ -260,6 +260,8 @@ constexpr PA_COMPONENT_EXPORT(
     PARTITION_ALLOC) bool DecommittedMemoryIsAlwaysZeroed() {
 #if BUILDFLAG(IS_APPLE)
   return false;
+#elif defined(NO_MADVISE_SYSCALL)
+  return false;
 #else
   return true;
 #endif

src/base/allocator/partition_allocator/page_allocator_internals_posix.h

@@ -410,6 +410,9 @@ void DiscardSystemPagesInternal(uintptr_t address, size_t length) {
     ret = madvise(ptr, length, MADV_DONTNEED);
   }
   PA_PCHECK(ret == 0);
+#elif defined(NO_MADVISE_SYSCALL)
+  static_cast<void>(ptr);
+  static_cast<void>(length);
 #else   // BUILDFLAG(IS_APPLE)
   // We have experimented with other flags, but with suboptimal results.
   //
@@ -417,12 +420,7 @@ void DiscardSystemPagesInternal(uintptr_t address, size_t length) {
   // performance benefits unclear.
   //
   // Therefore, we just do the simple thing: MADV_DONTNEED.
-  int ret = madvise(ptr, length, MADV_DONTNEED);
+  PA_PCHECK(0 == madvise(ptr, length, MADV_DONTNEED));
-  if (ret && errno == ENOSYS) {
-    // Ignores when the kernel is built without CONFIG_ADVISE_SYSCALLS
-    return;
-  }
-  PA_PCHECK(ret == 0);
 #endif  // BUILDFLAG(IS_APPLE)
 }
 

src/build/config/openwrt/BUILD.gn

@@ -14,6 +14,8 @@ assert(current_os == "openwrt")
 
 declare_args() {
   build_static = false
+
+  no_madvise_syscall = false
 }
 
 # This is included by reference in the //build/config/compiler config that
@@ -39,6 +41,10 @@ config("compiler") {
     ldflags += [ "-Wl,--dynamic-linker=/lib/ld-musl-mipsel-sf.so.1" ]
   }
 
+  if (no_madvise_syscall) {
+    defines += [ "NO_MADVISE_SYSCALL" ]
+  }
+
   abi = "musl"
   if (current_cpu == "arm") {
     abi = "muslgnueabi"