Files
build_soong/cc/config/x86_64_device.go
Kalesh Singh fa1ebf5943 soong: ldflags: Add separate-loadable-segments
To suport >4KB page sizes, the loader may extend LOAD segment mappings
to be contiguous in the virtual address space. This is done in order to
reduce the use of unreclaimable kernel slab memory for the otherwise
necessary gap VMAs (when the runtime-page-size < ELF-segment-p_align).

Such mappings may beyond the end of the backing file when extended;
which breaks the common userspace assumption that file memory maps are
entirely backed by the underlying file.

Existing apps (not yet updated for larger page size support) may
encounter breakages if they parse /proc/self/[s]maps and use the
[start, end] addresses to operate on system libraries that have
crt_pad_segment optimization (VMA extension) [1].

In order to avoid breaking exisiting apps, update the build system to
ensure the platform ELFs' segments are entirely backed by the file
even when the VMA is extended to be contiguous with the subsequent
segment's. This is achieved using the linker flag
-z separate-loadable-segments, which inserts enough padding (zeros)
to also align each segment's offset on file by it's p_align
(max-page-size).

Although laying out the ELF segments on disk to respect the p_align
causes an increase in the file's apparent size (i_size), on Android the
actual disk usage increase is not significant due to most of the padding
being zero blocks which don't get alloacted in the read-only partitions.

The following results were obtained on an ARM64 device on a recent
git_main build:

 No Separate     Separate     Delta         Delta %   Partition
   Loadable      Loadable
   Segments      Segments

   4208.90MB    4214.6MB       5.70MB       0.14%     All RO Partitions

Note: The overhead of -z separate-loadable-segments is minimized by the
fact that ARM64 android already builds with -z separate-code. [2]

[1] https://cs.android.com/android/platform/superproject/main/+/main:bionic/libc/arch-common/bionic/crt_pad_segment.S
[2] 733198152d:build/soong/cc/config/arm64_device.go;l=53

Bug: 328797737
Test: Manually test previously crashing application
Change-Id: Icb14ad10b5c9282855d54c7945b065b7b4184163
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
2024-03-12 17:04:50 -07:00

214 lines
5.3 KiB
Go

// Copyright 2015 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package config
import (
"fmt"
"strings"
"android/soong/android"
)
var (
x86_64Cflags = []string{
// Help catch common 32/64-bit errors.
"-Werror=implicit-function-declaration",
}
x86_64Cppflags = []string{}
x86_64Ldflags = []string{
"-Wl,--hash-style=gnu",
"-Wl,-z,separate-loadable-segments",
}
X86_64Lldflags = x86_64Ldflags
x86_64ArchVariantCflags = map[string][]string{
"": []string{
"-march=x86-64",
},
"broadwell": []string{
"-march=broadwell",
},
"goldmont": []string{
"-march=goldmont",
},
"goldmont-plus": []string{
"-march=goldmont-plus",
},
"goldmont-without-sha-xsaves": []string{
"-march=goldmont",
"-mno-sha",
"-mno-xsaves",
},
"haswell": []string{
"-march=core-avx2",
},
"ivybridge": []string{
"-march=core-avx-i",
},
"sandybridge": []string{
"-march=corei7",
},
"silvermont": []string{
"-march=slm",
},
"skylake": []string{
"-march=skylake",
},
"stoneyridge": []string{
"-march=bdver4",
},
"tremont": []string{
"-march=tremont",
},
}
x86_64ArchFeatureCflags = map[string][]string{
"ssse3": []string{"-mssse3"},
"sse4": []string{"-msse4"},
"sse4_1": []string{"-msse4.1"},
"sse4_2": []string{"-msse4.2"},
// Not all cases there is performance gain by enabling -mavx -mavx2
// flags so these flags are not enabled by default.
// if there is performance gain in individual library components,
// the compiler flags can be set in corresponding bp files.
// "avx": []string{"-mavx"},
// "avx2": []string{"-mavx2"},
// "avx512": []string{"-mavx512"}
"popcnt": []string{"-mpopcnt"},
"aes_ni": []string{"-maes"},
}
)
func init() {
exportedVars.ExportStringListStaticVariable("X86_64ToolchainCflags", []string{"-m64"})
exportedVars.ExportStringListStaticVariable("X86_64ToolchainLdflags", []string{"-m64"})
exportedVars.ExportStringListStaticVariable("X86_64Ldflags", x86_64Ldflags)
exportedVars.ExportStringList("X86_64Lldflags", X86_64Lldflags)
pctx.VariableFunc("X86_64Lldflags", func(ctx android.PackageVarContext) string {
maxPageSizeFlag := "-Wl,-z,max-page-size=" + ctx.Config().MaxPageSizeSupported()
flags := append(X86_64Lldflags, maxPageSizeFlag)
return strings.Join(flags, " ")
})
// Clang cflags
exportedVars.ExportStringList("X86_64Cflags", x86_64Cflags)
pctx.VariableFunc("X86_64Cflags", func(ctx android.PackageVarContext) string {
flags := x86_64Cflags
if ctx.Config().NoBionicPageSizeMacro() {
flags = append(flags, "-D__BIONIC_NO_PAGE_SIZE_MACRO")
}
return strings.Join(flags, " ")
})
exportedVars.ExportStringListStaticVariable("X86_64Cppflags", x86_64Cppflags)
// Yasm flags
exportedVars.ExportStringListStaticVariable("X86_64YasmFlags", []string{
"-f elf64",
"-m amd64",
})
// Extended cflags
exportedVars.ExportStringListDict("X86_64ArchVariantCflags", x86_64ArchVariantCflags)
exportedVars.ExportStringListDict("X86_64ArchFeatureCflags", x86_64ArchFeatureCflags)
// Architecture variant cflags
for variant, cflags := range x86_64ArchVariantCflags {
pctx.StaticVariable("X86_64"+variant+"VariantCflags", strings.Join(cflags, " "))
}
}
type toolchainX86_64 struct {
toolchainBionic
toolchain64Bit
toolchainCflags string
}
func (t *toolchainX86_64) Name() string {
return "x86_64"
}
func (t *toolchainX86_64) IncludeFlags() string {
return ""
}
func (t *toolchainX86_64) ClangTriple() string {
return "x86_64-linux-android"
}
func (t *toolchainX86_64) ToolchainLdflags() string {
return "${config.X86_64ToolchainLdflags}"
}
func (t *toolchainX86_64) ToolchainCflags() string {
return t.toolchainCflags
}
func (t *toolchainX86_64) Cflags() string {
return "${config.X86_64Cflags}"
}
func (t *toolchainX86_64) Cppflags() string {
return "${config.X86_64Cppflags}"
}
func (t *toolchainX86_64) Ldflags() string {
return "${config.X86_64Ldflags}"
}
func (t *toolchainX86_64) Lldflags() string {
return "${config.X86_64Lldflags}"
}
func (t *toolchainX86_64) YasmFlags() string {
return "${config.X86_64YasmFlags}"
}
func (toolchainX86_64) LibclangRuntimeLibraryArch() string {
return "x86_64"
}
func x86_64ToolchainFactory(arch android.Arch) Toolchain {
// Error now rather than having a confusing Ninja error
if _, ok := x86_64ArchVariantCflags[arch.ArchVariant]; !ok {
panic(fmt.Sprintf("Unknown x86_64 architecture version: %q", arch.ArchVariant))
}
toolchainCflags := []string{
"${config.X86_64ToolchainCflags}",
"${config.X86_64" + arch.ArchVariant + "VariantCflags}",
}
for _, feature := range arch.ArchFeatures {
toolchainCflags = append(toolchainCflags, x86_64ArchFeatureCflags[feature]...)
}
return &toolchainX86_64{
toolchainCflags: strings.Join(toolchainCflags, " "),
}
}
func init() {
registerToolchainFactory(android.Android, android.X86_64, x86_64ToolchainFactory)
}