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Mirror of unofficial glibc git repository located at git://sourceware.org/git/glibc.git

License: GNU General Public License v2.0

Roff 3.32% Makefile 0.88% C 66.48% C++ 9.16% Python 0.78% Shell 0.42% Awk 0.09% M4 0.16% Assembly 13.72% Objective-C 4.34% Yacc 0.01% Perl 0.04% TeX 0.52% sed 0.01% Pawn 0.07%

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glibc's Issues

ELF Loading

Please see elf/dl-load.c

glibc/elf/dl-load.c

Lines 1031 to 1196 in 56c86f5

/* On most platforms presume that PT_GNU_STACK is absent and the stack is
* executable. Other platforms default to a nonexecutable stack and don't
* need PT_GNU_STACK to do so. */
uint_fast16_t stack_flags = DEFAULT_STACK_PERMS;
{
/* Scan the program header table, collecting its load commands. */
struct loadcmd loadcmds[l->l_phnum];
size_t nloadcmds = 0;
bool has_holes = false;
/* The struct is initialized to zero so this is not necessary:
l->l_ld = 0;
l->l_phdr = 0;
l->l_addr = 0; */
for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
switch (ph->p_type)
{
/* These entries tell us where to find things once the file's
segments are mapped in. We record the addresses it says
verbatim, and later correct for the run-time load address. */
case PT_DYNAMIC:
if (ph->p_filesz)
{
/* Debuginfo only files from "objcopy --only-keep-debug"
contain a PT_DYNAMIC segment with p_filesz == 0. Skip
such a segment to avoid a crash later. */
l->l_ld = (void *) ph->p_vaddr;
l->l_ldnum = ph->p_memsz / sizeof (ElfW(Dyn));
}
break;
case PT_PHDR:
l->l_phdr = (void *) ph->p_vaddr;
break;
case PT_LOAD:
/* A load command tells us to map in part of the file.
We record the load commands and process them all later. */
if (__glibc_unlikely ((ph->p_align & (GLRO(dl_pagesize) - 1)) != 0))
{
errstring = N_("ELF load command alignment not page-aligned");
goto call_lose;
}
if (__glibc_unlikely (((ph->p_vaddr - ph->p_offset)
& (ph->p_align - 1)) != 0))
{
errstring
= N_("ELF load command address/offset not properly aligned");
goto call_lose;
}
struct loadcmd *c = &loadcmds[nloadcmds++];
c->mapstart = ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize));
c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
c->dataend = ph->p_vaddr + ph->p_filesz;
c->allocend = ph->p_vaddr + ph->p_memsz;
c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
/* Determine whether there is a gap between the last segment
and this one. */
if (nloadcmds > 1 && c[-1].mapend != c->mapstart)
has_holes = true;
/* Optimize a common case. */
#if (PF_R | PF_W | PF_X) == 7 && (PROT_READ | PROT_WRITE | PROT_EXEC) == 7
c->prot = (PF_TO_PROT
>> ((ph->p_flags & (PF_R | PF_W | PF_X)) * 4)) & 0xf;
#else
c->prot = 0;
if (ph->p_flags & PF_R)
c->prot |= PROT_READ;
if (ph->p_flags & PF_W)
c->prot |= PROT_WRITE;
if (ph->p_flags & PF_X)
c->prot |= PROT_EXEC;
#endif
break;
case PT_TLS:
if (ph->p_memsz == 0)
/* Nothing to do for an empty segment. */
break;
l->l_tls_blocksize = ph->p_memsz;
l->l_tls_align = ph->p_align;
if (ph->p_align == 0)
l->l_tls_firstbyte_offset = 0;
else
l->l_tls_firstbyte_offset = ph->p_vaddr & (ph->p_align - 1);
l->l_tls_initimage_size = ph->p_filesz;
/* Since we don't know the load address yet only store the
offset. We will adjust it later. */
l->l_tls_initimage = (void *) ph->p_vaddr;
/* If not loading the initial set of shared libraries,
check whether we should permit loading a TLS segment. */
if (__glibc_likely (l->l_type == lt_library)
/* If GL(dl_tls_dtv_slotinfo_list) == NULL, then rtld.c did
not set up TLS data structures, so don't use them now. */
|| __glibc_likely (GL(dl_tls_dtv_slotinfo_list) != NULL))
{
/* Assign the next available module ID. */
l->l_tls_modid = _dl_next_tls_modid ();
break;
}
#ifdef SHARED
/* We are loading the executable itself when the dynamic
linker was executed directly. The setup will happen
later. Otherwise, the TLS data structures are already
initialized, and we assigned a TLS modid above. */
assert (l->l_prev == NULL || (mode & __RTLD_AUDIT) != 0);
#else
assert (false && "TLS not initialized in static application");
#endif
break;
case PT_GNU_STACK:
stack_flags = ph->p_flags;
break;
case PT_GNU_RELRO:
l->l_relro_addr = ph->p_vaddr;
l->l_relro_size = ph->p_memsz;
break;
case PT_NOTE:
if (_dl_process_pt_note (l, ph, fd, fbp))
{
errstring = N_("cannot process note segment");
goto call_lose;
}
break;
}
if (__glibc_unlikely (nloadcmds == 0))
{
/* This only happens for a bogus object that will be caught with
another error below. But we don't want to go through the
calculations below using NLOADCMDS - 1. */
errstring = N_("object file has no loadable segments");
goto call_lose;
}
if (__glibc_unlikely (type != ET_DYN)
&& __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0))
{
/* This object is loaded at a fixed address. This must never
happen for objects loaded with dlopen. */
errstring = N_("cannot dynamically load executable");
goto call_lose;
}
/* Length of the sections to be loaded. */
maplength = loadcmds[nloadcmds - 1].allocend - loadcmds[0].mapstart;
/* Now process the load commands and map segments into memory.
This is responsible for filling in:
l_map_start, l_map_end, l_addr, l_contiguous, l_text_end, l_phdr
*/
errstring = _dl_map_segments (l, fd, header, type, loadcmds, nloadcmds,
maplength, has_holes, loader);
if (__glibc_unlikely (errstring != NULL))
goto call_lose;
}

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