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// Copyright (c) 2020 Johannes Stoelp
#include <auxv.h>
#include <elf.h>
#include <io.h>
#if !defined(__linux__) || !defined(__x86_64__)
# error "Only supported in linux(x86_64)!"
#endif
void entry(const uint64_t* prctx) {
// Interpret data on the stack passed by the OS kernel as specified in the
// x86_64 SysV ABI.
uint64_t argc = *prctx;
const char** argv = (const char**)(prctx + 1);
const char** envv = (const char**)(argv + argc + 1);
// Count the number of environment variables in the `ENVP` segment.
int envc = 0;
for (const char** env = envv; *env; ++env) {
++envc;
}
uint64_t auxv[AT_MAX_CNT];
for (unsigned i = 0; i < AT_MAX_CNT; ++i) {
auxv[i] = 0;
}
// Read the `AUXV` auxiliary vector segment.
const Auxv64Entry* auxvp = (const Auxv64Entry*)(envv + envc + 1);
for (; auxvp->tag != AT_NULL; ++auxvp) {
if (auxvp->tag < AT_MAX_CNT) {
auxv[auxvp->tag] = auxvp->val;
}
}
// Print the data provided by the Linux Kernel on the stack.
pfmt("Got %d arg(s)\n", argc);
for (const char** arg = argv; *arg; ++arg) {
pfmt("\targ = %s\n", *arg);
}
const int max_env = 10;
pfmt("Print first %d env var(s)\n", max_env - 1);
for (const char** env = envv; *env && (env - envv < max_env); ++env) {
pfmt("\tenv = %s\n", *env);
}
pfmt("Print auxiliary vector\n");
pfmt("\tAT_EXECFD: %ld\n", auxv[AT_EXECFD]);
pfmt("\tAT_PHDR : %p\n", auxv[AT_PHDR]);
pfmt("\tAT_PHENT : %ld\n", auxv[AT_PHENT]);
pfmt("\tAT_PHNUM : %ld\n", auxv[AT_PHNUM]);
pfmt("\tAT_PAGESZ: %ld\n", auxv[AT_PAGESZ]);
pfmt("\tAT_BASE : %lx\n", auxv[AT_BASE]);
pfmt("\tAT_FLAGS : %ld\n", auxv[AT_FLAGS]);
pfmt("\tAT_ENTRY : %p\n", auxv[AT_ENTRY]);
pfmt("\tAT_NOTELF: %lx\n", auxv[AT_NOTELF]);
pfmt("\tAT_UID : %ld\n", auxv[AT_UID]);
pfmt("\tAT_EUID : %ld\n", auxv[AT_EUID]);
pfmt("\tAT_GID : %ld\n", auxv[AT_GID]);
pfmt("\tAT_EGID : %ld\n", auxv[AT_EGID]);
}
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