gdb/testsuite/gdb.base/rtld-step.exp

# Copyright 2022-2024 Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# Test stepping through a runtime loader / dynamic linker (RTLD):
#
# While it'd be nice to have a test which steps through an actual
# runtime loader / dynamic linker, constructing such a test would be
# non-portable; we would need to know implementation details such
# as the names of some of the symbols and the order of calls to
# various functions that implement the RTLD.  So, instead, we'll use a
# program which doesn't even pretend to implement this functionality,
# but which will instead be invoked in the same fashion (for ELF
# binaries anyway) as would be expected for an ELF-based RTLD.
#
# To that end, we have two programs, one which will pretend to be an
# RTLD and the other which will be caused to use the pretend RTLD.
#
# When the main program is run, the pretend/fake RTLD is run instead,
# due to it being specified as the ELF interpreter for the main
# program.  Within GDB, we then attempt to do some simple debugging
# involving 'step', 'next', and 'finish'.

# This test can't be run on targets lacking shared library support
# or for non-ELF targets.  (We're not really testing or building
# shared libraries here, but having a RTLD implies having shared
# libraries on the target.)
require allow_shlib_tests is_elf_target

# (Pretend) RTLD file names and flags:
set rtld_basename ${::gdb_test_file_name}-rtld
set srcfile_rtld ${srcdir}/${subdir}/${rtld_basename}.c
set binfile_rtld [standard_output_file ${rtld_basename}]

# Placing 'pie' in the flag list (for rtld_flags) doesn't work, but
# using -static-pie -FPIE in additional_flags does.  Apparently, when
# 'pie' is listed, gdb_compile will (on Linux) use both -fPIE and
# -pie.	 Testing shows that use of -pie creates a dynamically linked
# executable when either a static or static-pie executable is desired
# instead.  (This is probably fragile.)
#
# While developing this code on Fedora Linux, it was found that (only)
# the flags -static-pie -fPIE were needed for Fedora 35 through Fedora
# 38.  The source file rtld-step-rtld.c didn't need the _start()
# function either.  And, better still, it was possible to call
# printf() to output progress messages in the pretend/fake RTLD. 
# Sadly, these output statements had to be removed in order to obtain
# code which would work on other Linux distributions / releases.
#
# When testing against earlier versions of Fedora, RHEL 9, and
# also Ubuntu 22.04, that short flag list didn't work.	For these
# linux releases, it was found that -nostdlib -lc were also required.
# Due to the use of -nostdlib, a _start() function had to be added
# to the RTLD code.
#
# Finally, on FreeBSD, it was found that in order to end up with a
# statically linked executable, -static was also needed.
# Unfortunately, when attempting to run the rtld-step-main under GDB
# on FreeBSD 13.1, this message was/is encountered:
#
# ELF interpreter /path/to/rtld-step-rtld not found, error 22
#
# So, sadly, this test does not currently work on FreeBSD.  If you try
# to make it work on FreeBSD, you'll probably need to enable the
# declarations for __progname and environ in rtld-step-rtld.c.
#
# If this test becomes broken at some point in the future, you might
# try removing -static from the flags below as it is not needed for
# Linux.
#
# Also, because the RTLD is static, you'll need static versions of
# libc/glibc installed on your system.  (A message such as "cannot
# find -lc" is a clue that you're missing a static version of libc.)

set rtld_flags [list debug additional_flags=[list -static-pie -fPIE \
						  -nostdlib -static -lc]]

if { ![gdb_can_simple_compile static-pie-static-libc \
	   "void _start (void) { _exit (0); }" \
	   executable $rtld_flags] } {
    set reason "-static-pie not supported or static libc missing"
    untested "failed to compile ($reason)"
    return -1
}

# Main program file names and flags:
set main_basename ${::gdb_test_file_name}-main
set srcfile_main ${srcdir}/${subdir}/${main_basename}.c
set binfile_main [standard_output_file ${main_basename}]
set main_flags [list debug additional_flags="-Wl,--dynamic-linker=${binfile_rtld}"]

# Compile pretend RTLD:
if { [gdb_compile ${srcfile_rtld} ${binfile_rtld} executable $rtld_flags] != "" } {
    untested "failed to compile"
    return -1
}

# Compile main program:
if { [gdb_compile ${srcfile_main} ${binfile_main} executable $main_flags] != "" } {
    untested "failed to compile"
    return -1
}

clean_restart ${binfile_main}

if {![runto_main]} {
    return 0
}

# Running the command 'info sharedlibrary' should output a path to
# the pretend/fake RTLD along with the address range.  Check that
# this path is present and, if so, extract the address range.
gdb_test_multiple "info sharedlibrary" "" {
    -re -wrap "($hex)\[ \t\]+($hex)\[ \t\]+Yes\[ \t\]+$fullname_syntax$rtld_basename" {
	set rtld_lower $expect_out(1,string)
	set rtld_upper $expect_out(2,string)
	pass $gdb_test_name
    }
}

# Fetch PC value.
set pc [get_hexadecimal_valueof "\$pc" 0]

# Verify that PC is in the address range of the pretend/fake RTLD.
gdb_assert { $rtld_lower <= $pc && $pc < $rtld_upper } "pc is in rtld"

gdb_test "next" {bar \(\);} "next over foo 0"
gdb_test "step" {bar \(\) at.*foo \(1\);.*} "step into bar"
gdb_test "step" {baz \(.*?\);} "step into foo 1"
gdb_test "finish" {Run till exit.*bar \(\).*baz.*} "finish out of foo 1"
gdb_test "next" {foo \(2\);} "next over baz in bar"
gdb_test "step" {baz \(.*?\);} "step into foo 2"
gdb_test "next" "\}" "next over baz in foo"
gdb_test "step" "bar \\(\\).*}" "step out of foo back into bar"

gdb_continue_to_end