dergrimm/getauxval-backport
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Add zig build system

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This commit is contained in:
Dominic Grimm 2025-02-11 17:53:20 +01:00
parent e11b6cc0b3
commit 0038ff7254
5 changed files with 259 additions and 51 deletions
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22
.gitignore vendored Normal file
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# This file is for zig-specific build artifacts.
# If you have OS-specific or editor-specific files to ignore,
# such as *.swp or .DS_Store, put those in your global
# ~/.gitignore and put this in your ~/.gitconfig:
#
# [core]
# excludesfile = ~/.gitignore
#
# Cheers!
# -andrewrk
.zig-cache/
zig-out/
/release/
/debug/
/build/
/build-*/
/docgen_tmp/
# Although this was renamed to .zig-cache, let's leave it here for a few
# releases to make it less annoying to work with multiple branches.
zig-cache/

98
build.zig Normal file
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const std = @import("std");
// Although this function looks imperative, note that its job is to
// declaratively construct a build graph that will be executed by an external
// runner.
pub fn build(b: *std.Build) void {
// Standard target options allows the person running `zig build` to choose
// what target to build for. Here we do not override the defaults, which
// means any target is allowed, and the default is native. Other options
// for restricting supported target set are available.
const target = b.standardTargetOptions(.{});
// Standard optimization options allow the person running `zig build` to select
// between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
// set a preferred release mode, allowing the user to decide how to optimize.
const optimize = b.standardOptimizeOption(.{});
const opt_elf64 = b.option(bool, "elf64", "ELF 64 bit").?;
const opt_file = b.option(bool, "file", "Get auxiliary vectors from /proc/self/auxv") orelse false;
const lib = b.addStaticLibrary(.{
.name = "getauxval-backport",
.target = target,
.optimize = optimize,
});
lib.linkLibC();
lib.addCSourceFile(.{
.file = b.path("src/getauxval_backport.c"),
.flags = &.{
if (!opt_elf64) "-DGETAUXVAL_BACKPORT_ELF32" else "",
if (opt_file) "-DGETAUXVAL_BACKPORT_FILE" else "",
},
});
b.installArtifact(lib);
// const exe = b.addExecutable(.{
// .name = "getauxval-backport",
// .root_source_file = b.path("src/main.zig"),
// .target = target,
// .optimize = optimize,
// });
// // This declares intent for the executable to be installed into the
// // standard location when the user invokes the "install" step (the default
// // step when running `zig build`).
// b.installArtifact(exe);
// // This *creates* a Run step in the build graph, to be executed when another
// // step is evaluated that depends on it. The next line below will establish
// // such a dependency.
// const run_cmd = b.addRunArtifact(exe);
// // By making the run step depend on the install step, it will be run from the
// // installation directory rather than directly from within the cache directory.
// // This is not necessary, however, if the application depends on other installed
// // files, this ensures they will be present and in the expected location.
// run_cmd.step.dependOn(b.getInstallStep());
// // This allows the user to pass arguments to the application in the build
// // command itself, like this: `zig build run -- arg1 arg2 etc`
// if (b.args) |args| {
// run_cmd.addArgs(args);
// }
// // This creates a build step. It will be visible in the `zig build --help` menu,
// // and can be selected like this: `zig build run`
// // This will evaluate the `run` step rather than the default, which is "install".
// const run_step = b.step("run", "Run the app");
// run_step.dependOn(&run_cmd.step);
// // Creates a step for unit testing. This only builds the test executable
// // but does not run it.
// const lib_unit_tests = b.addTest(.{
// .root_source_file = b.path("src/root.zig"),
// .target = target,
// .optimize = optimize,
// });
// const run_lib_unit_tests = b.addRunArtifact(lib_unit_tests);
// const exe_unit_tests = b.addTest(.{
// .root_source_file = b.path("src/main.zig"),
// .target = target,
// .optimize = optimize,
// });
// const run_exe_unit_tests = b.addRunArtifact(exe_unit_tests);
// // Similar to creating the run step earlier, this exposes a `test` step to
// // the `zig build --help` menu, providing a way for the user to request
// // running the unit tests.
// const test_step = b.step("test", "Run unit tests");
// test_step.dependOn(&run_lib_unit_tests.step);
// test_step.dependOn(&run_exe_unit_tests.step);
}

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build.zig.zon Normal file
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.{
// This is the default name used by packages depending on this one. For
// example, when a user runs `zig fetch --save <url>`, this field is used
// as the key in the `dependencies` table. Although the user can choose a
// different name, most users will stick with this provided value.
//
// It is redundant to include "zig" in this name because it is already
// within the Zig package namespace.
.name = "getauxval-backport",
// This is a [Semantic Version](https://semver.org/).
// In a future version of Zig it will be used for package deduplication.
.version = "0.0.0",
// This field is optional.
// This is currently advisory only; Zig does not yet do anything
// with this value.
//.minimum_zig_version = "0.11.0",
// This field is optional.
// Each dependency must either provide a `url` and `hash`, or a `path`.
// `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
// Once all dependencies are fetched, `zig build` no longer requires
// internet connectivity.
.dependencies = .{
// See `zig fetch --save <url>` for a command-line interface for adding dependencies.
//.example = .{
// // When updating this field to a new URL, be sure to delete the corresponding
// // `hash`, otherwise you are communicating that you expect to find the old hash at
// // the new URL.
// .url = "https://example.com/foo.tar.gz",
//
// // This is computed from the file contents of the directory of files that is
// // obtained after fetching `url` and applying the inclusion rules given by
// // `paths`.
// //
// // This field is the source of truth; packages do not come from a `url`; they
// // come from a `hash`. `url` is just one of many possible mirrors for how to
// // obtain a package matching this `hash`.
// //
// // Uses the [multihash](https://multiformats.io/multihash/) format.
// .hash = "...",
//
// // When this is provided, the package is found in a directory relative to the
// // build root. In this case the package's hash is irrelevant and therefore not
// // computed. This field and `url` are mutually exclusive.
// .path = "foo",
// // When this is set to `true`, a package is declared to be lazily
// // fetched. This makes the dependency only get fetched if it is
// // actually used.
// .lazy = false,
//},
},
// Specifies the set of files and directories that are included in this package.
// Only files and directories listed here are included in the `hash` that
// is computed for this package. Only files listed here will remain on disk
// when using the zig package manager. As a rule of thumb, one should list
// files required for compilation plus any license(s).
// Paths are relative to the build root. Use the empty string (`""`) to refer to
// the build root itself.
// A directory listed here means that all files within, recursively, are included.
.paths = .{
"build.zig",
"build.zig.zon",
"src",
// For example...
//"LICENSE",
//"README.md",
},
}

51
getauxval.c
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#include <stdio.h>
#include <sys/auxv.h>
#ifdef GETAUXVAL_BACKPORT_ELF64
typedef Elf64_auxv_t __auxv_t;
#else
typedef Elf32_auxv_t __auxv_t;
#endif
#define AUXV_FILE "/proc/self/auxv"
unsigned long getauxval(unsigned long type) {
#ifdef GETAUXVAL_BACKPORT_DEBUG
printf("getauxval: search started for type: %lu\n", type);
#endif
FILE *f = fopen(AUXV_FILE, "rb");
if (f == NULL)
return 1;
unsigned long val = AT_NULL;
__auxv_t aux;
#ifdef GETAUXVAL_BACKPORT_DEBUG
unsigned int i = 0;
#endif
while (fread(&aux, sizeof(aux), 1, f) == 1 && aux.a_type != AT_NULL) {
#ifdef GETAUXVAL_BACKPORT_DEBUG
printf("getauxval: current type: %u [%u]\n", aux.a_type, i);
#endif
if (aux.a_type == type) {
#ifdef GETAUXVAL_BACKPORT_DEBUG
printf("getauxval: found %u with value: 0x%x\n", aux.a_type,
aux.a_un.a_val);
#endif
val = aux.a_un.a_val;
break;
}
#ifdef GETAUXVAL_BACKPORT_DEBUG
i++;
#endif
}
fclose(f);
return val;
}

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src/getauxval_backport.c Normal file
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#include <elf.h>
#include <stddef.h>
#include <stdio.h>
#ifdef GETAUXVAL_BACKPORT_ELF64
typedef Elf64_auxv_t __auxv_t;
#else
typedef Elf32_auxv_t __auxv_t;
#endif
#define AUXV_FILE "/proc/self/auxv"
#ifdef GETAUXVAL_BACKPORT_FILE
unsigned long __getauxval_file(unsigned long type) {
FILE *f = fopen(AUXV_FILE, "rb");
if (f == NULL)
return 1;
unsigned long val = 0;
__auxv_t aux;
while (fread(&aux, sizeof(aux), 1, f) == 1 && aux.a_type != AT_NULL) {
if (aux.a_type == type) {
val = aux.a_un.a_val;
break;
}
}
fclose(f);
return val;
}
#else
extern char **environ;
char **envp_auxv = NULL;
unsigned long __getauxval_envp(unsigned long type) {
if (envp_auxv == NULL) {
envp_auxv = environ;
while (*envp_auxv++ != NULL)
;
}
__auxv_t *auxv;
for (auxv = (__auxv_t *)envp_auxv; auxv->a_type != AT_NULL; auxv++) {
if (auxv->a_type == type) {
return auxv->a_un.a_val;
}
}
return 0;
}
#endif
unsigned long getauxval(unsigned long type) {
#ifdef GETAUXVAL_BACKPORT_FILE
return __getauxval_file(type);
#else
return __getauxval_envp(type);
#endif
}