This changes the TLS offset calculation logic to be based on the
symbol's size instead of the total size of the TLS.
Because of this change, we no longer need to pipe "m_tls_size" to so
many functions.
Also, After this patch, the TLS data of the main program exists at the
"end" of the TLS block (Highest addresses).
This fixes a part of #6609.
Previously, TLS data was always zero-initialized.
To support initializing the values of TLS data, sys$allocate_tls now
receives a buffer with the desired initial data, and copies it to the
master TLS region of the process.
The DynamicLinker gathers the initial TLS image and passes it to
sys$allocate_tls.
We also now require the size passed to sys$allocate_tls to be
page-aligned, to make things easier. Note that this doesn't waste memory
as the TLS data has to be allocated in separate pages anyway.
This fixes a regression that was introduced in f40ee1b and caused the
tls_offset of all objects other than the main program to be 0.
After this fix map_library's is_program argument is no longer used, so
it was removed.
We had some inconsistencies before:
- Sometimes "The", sometimes "the"
- Sometimes trailing ".", sometimes no trailing "."
I picked the most common one (lowecase "the", trailing ".") and applied
it to all copyright headers.
By using the exact same string everywhere we can ensure nothing gets
missed during a global search (and replace), and that these
inconsistencies are not spread any further (as copyright headers are
commonly copied to new files).
This implements more of the dlfcn functionality. Most notably:
* It's now possible to dlopen() libraries which were already
loaded at program startup time. This does not cause those
libraries to be loaded twice.
* Errors are reported via dlerror() rather than by crashing
the program.
* Calls to the dl*() functions are thread-safe.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
The shared library libicudata.so has a DT_SYMBOLIC entry:
Dynamic Section:
NEEDED libgcc_s.so
SONAME libicudata.so.69
SYMBOLIC 0x00000000
HASH 0x00000094
STRTAB 0x000000c8
SYMTAB 0x000000a8
STRSZ 0x0000002a
SYMENT 0x00000010
According to the ELF spec DT_SYMBOLIC has no special meaning
for the dynamic loader.
The calculation for TLS relocations was incorrect which would
result in overlapping TLS variables when more than one shared
object used TLS variables.
This bug can be reproduced with a shared library and a program
like this:
$ cat tlstest.c
#include <string.h>
__thread char tls_val[1024];
void set_val() { memset(tls_val, 0, sizeof(tls_val)); }
$ gcc -g -shared -o usr/lib/libtlstest.so tlstest.c
$ cat test.c
void set_val();
int main() { set_val(); }
$ gcc -g -o tls test.c -ltlstest
Due to the way the TLS relocations are done this program would
clobber libc's TLS variables (e.g. errno).
Mostly due to the fact that clang-format allows aligned comments via
AlignTrailingComments.
We could also use raw string literals in inline asm, which clang-format
deals with properly (and would be nicer in a lot of places).
Merge the load_elf() and commit_elf() functions into a single
load_main_executable() function that takes care of both things.
Also split "stage 3" into two separate stages, keeping the lazy
relocations in stage 3, and adding a stage 4 for calling library
initialization functions.
We also make sure to map the main executable before dealing with
any of its dependencies, to ensure that non-PIE executables get
loaded at their desired address.
Instead of having a special case in the dynamic loader where we ignore
TM-related GCC symbols, just stub them out in LibC like we already do
for various other things we don't support.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
The name-to-section lookup table was only used in a handful of places,
and none of them were calling it nearly enough to justify building
a cache for it in the first place. So let's get rid of it and reduce
startup time by a little bit. :^)
It's a lot faster to iterate the GNU hash tables if we don't have to
compute the length of every symbol name before rejecting it anyway while
comparing the first character. :^)
When performing a global symbol lookup, we were recomputing the symbol
hashes once for every dynamic object searched. The hash function was
at the very top of a profile (15%) of program startup.
With this change, the hash function is no longer visible among the top
stacks in the profile. :^)
This logging mode was unusable anyway since it spams way too much.
The dynamic loader is in a pretty good place now anyway, so I think
it's okay for us to drop some of the bring-up debug logging. :^)
Also, we have to be careful with dbgln_if(FOO_DEBUG, "{}", foo())
where foo() is something expensive, since it might get evaluated
even if !FOO_DEBUG.
Let's use a stronger type than void* for this since we're talking
specifically about a virtual address and not necessarily a pointer
to something actually in memory (yet).
It was very confusing how these functions used the "undefined" state
of Symbol to signal lookup failure. Let's use Optional<T> to make things
a bit more understandable.
