diff options
| -rw-r--r-- | 04_dynld_nostd/dynld.c | 49 |
1 files changed, 25 insertions, 24 deletions
diff --git a/04_dynld_nostd/dynld.c b/04_dynld_nostd/dynld.c index 6e1bebf..5193761 100644 --- a/04_dynld_nostd/dynld.c +++ b/04_dynld_nostd/dynld.c @@ -21,7 +21,7 @@ enum { }; // }}} -// {{{ Execinfo +// {{{ SystemVDescriptor typedef struct { uint64_t argc; // Number of commandline arguments. @@ -29,31 +29,31 @@ typedef struct { uint64_t envc; // Number of environment variables. const char** envv; // List of pointers to environment variables. uint64_t auxv[AT_MAX_CNT]; // Auxiliary vector entries. -} ExecInfo; +} SystemVDescriptor; // Interpret and extract data passed on the stack by the Linux Kernel // when loading the initial process image. // The data is organized according to the SystemV x86_64 ABI. -static ExecInfo get_exec_info(const uint64_t* prctx) { - ExecInfo info = {0}; +static SystemVDescriptor get_systemv_descriptor(const uint64_t* prctx) { + SystemVDescriptor sysv = {0}; - info.argc = *prctx; - info.argv = (const char**)(prctx + 1); - info.envv = (const char**)(info.argv + info.argc + 1); + sysv.argc = *prctx; + sysv.argv = (const char**)(prctx + 1); + sysv.envv = (const char**)(sysv.argv + sysv.argc + 1); // Count the number of environment variables in the `ENVP` segment. - for (const char** env = info.envv; *env; ++env) { - info.envc += 1; + for (const char** env = sysv.envv; *env; ++env) { + sysv.envc += 1; } // Decode auxiliary vector `AUXV`. - for (const Auxv64Entry* auxvp = (const Auxv64Entry*)(info.envv + info.envc + 1); auxvp->tag != AT_NULL; ++auxvp) { + for (const Auxv64Entry* auxvp = (const Auxv64Entry*)(sysv.envv + sysv.envc + 1); auxvp->tag != AT_NULL; ++auxvp) { if (auxvp->tag < AT_MAX_CNT) { - info.auxv[auxvp->tag] = auxvp->val; + sysv.auxv[auxvp->tag] = auxvp->val; } } - return info; + return sysv; } // }}} @@ -92,7 +92,7 @@ static void decode_dynamic(Dso* dso, uint64_t dynoff) { ERROR_ON(dso->dynamic[DT_HASH] == 0, "DT_HASH missing in dynamic section!"); } -static Dso get_prog_dso(const ExecInfo* info) { +static Dso get_prog_dso(const SystemVDescriptor* sysv) { Dso prog = {0}; // Determine the base address of the user program. @@ -121,21 +121,21 @@ static Dso get_prog_dso(const ExecInfo* info) { // | | // // PROG BASE = AT_PHDR - PT_PHDR.vaddr - ERROR_ON(info->auxv[AT_PHDR] == 0 || info->auxv[AT_EXECFD] != 0, "AT_PHDR entry missing in the AUXV!"); + ERROR_ON(sysv->auxv[AT_PHDR] == 0 || sysv->auxv[AT_EXECFD] != 0, "AT_PHDR entry missing in the AUXV!"); // Offset to the `.dynamic` section from the user programs `base addr`. uint64_t dynoff = 0; // Program header of the user program. - const Elf64Phdr* phdr = (const Elf64Phdr*)info->auxv[AT_PHDR]; + const Elf64Phdr* phdr = (const Elf64Phdr*)sysv->auxv[AT_PHDR]; - ERROR_ON(info->auxv[AT_PHENT] != sizeof(Elf64Phdr), "Elf64Phdr size miss-match!"); + ERROR_ON(sysv->auxv[AT_PHENT] != sizeof(Elf64Phdr), "Elf64Phdr size miss-match!"); // Decode PHDRs of the user program. - for (unsigned phdrnum = info->auxv[AT_PHNUM]; --phdrnum; ++phdr) { + for (unsigned phdrnum = sysv->auxv[AT_PHNUM]; --phdrnum; ++phdr) { if (phdr->type == PT_PHDR) { - ERROR_ON(info->auxv[AT_PHDR] < phdr->vaddr, "Expectation auxv[AT_PHDR] >= phdr->vaddr failed!"); - prog.base = (uint8_t*)(info->auxv[AT_PHDR] - phdr->vaddr); + ERROR_ON(sysv->auxv[AT_PHDR] < phdr->vaddr, "Expectation auxv[AT_PHDR] >= phdr->vaddr failed!"); + prog.base = (uint8_t*)(sysv->auxv[AT_PHDR] - phdr->vaddr); } else if (phdr->type == PT_DYNAMIC) { dynoff = phdr->vaddr; } @@ -148,8 +148,8 @@ static Dso get_prog_dso(const ExecInfo* info) { decode_dynamic(&prog, dynoff); // Get the entrypoint of the user program form the auxiliary vector. - ERROR_ON(info->auxv[AT_ENTRY] == 0, "AT_ENTRY entry missing in the AUXV!"); - prog.entry = (void (*)())info->auxv[AT_ENTRY]; + ERROR_ON(sysv->auxv[AT_ENTRY] == 0, "AT_ENTRY entry missing in the AUXV!"); + prog.entry = (void (*)())sysv->auxv[AT_ENTRY]; return prog; } @@ -265,6 +265,7 @@ static void* lookup_sym(const Dso* dso, const char* symname) { static Dso map_dependency(const char* dependency) { // For simplicity we only search for SO dependencies in the current working dir. + // So no support for DT_RPATH/DT_RUNPATH and LD_LIBRARY_PATH. ERROR_ON(access(dependency, R_OK) != 0, "Dependency '%s' does not exist!\n", dependency); const int fd = open(dependency, O_RDONLY); @@ -524,14 +525,14 @@ static void setup_got(const Dso* dso) { void dl_entry(const uint64_t* prctx) { // Parse SystemV ABI block. - const ExecInfo exec_info = get_exec_info(prctx); + const SystemVDescriptor sysv_desc = get_systemv_descriptor(prctx); // Ensure hard-coded page size value is correct. - ERROR_ON(exec_info.auxv[AT_PAGESZ] != PAGE_SIZE, "Hard-coded PAGE_SIZE miss-match!"); + ERROR_ON(sysv_desc.auxv[AT_PAGESZ] != PAGE_SIZE, "Hard-coded PAGE_SIZE miss-match!"); // Initialize dso handle for user program but extracting necesarry // information from `AUXV` and the `PHDR`. - const Dso dso_prog = get_prog_dso(&exec_info); + const Dso dso_prog = get_prog_dso(&sysv_desc); // Map dependency. // |