mirror of
https://github.com/espressif/binutils-gdb.git
synced 2025-06-23 19:50:13 +08:00
38cf168be5
What a trip down a rabbit hole this bug has been. First observation: You can't use deferred_expression in s_leb128. deferred_expression implements the semantics of .eqv or '==', saving an expression with minimal simplification for assignment to a symbol so that the expression is evaluated at uses of the symbol. In particular, the value of "dot" is not evaluated at the .eqv symbol assignment, but later. When s_leb128 uses deferred_expression, "later" is at the end of assembly, giving entirely the wrong value of "dot". There is no way to fix this for the s_leb128 use without breaking .equ (which incidentally was already somewhat broken, see commit e4c2619ad1). So, don't use deferred_expression in s_leb128. But that leads to the gas test elf/dwarf2-17 failing, because view symbols are calculated with a chain of expression symbols. In the dwarf2-17 .L1 case there is a "temp_sym_1 > temp_sym_2" expression, with temp_sym_1 and temp_sym_2 on either side of a ".balign". Since ".balign" and many other directives moving "dot" are not calculated on the first (and only) pass over source, .L1 cannot be calculated until final addresses are assigned to frags. However, ".uleb128 .L1" *is* calculated immediately, resulting in the wrong value. The reason why .L1 is calculated immediately is that code in expr.c:operand after the comment /* If we have an absolute symbol or a reg, then we know its value now. */ does as it says and fixes the value of .L1, because .L1 is assigned to absolute_section in dwarf2dbg.c:set_or_check_view. So, correct that to expr_section. Unfortunately that fix leads to failure of the elf/dwarf2-5 test with ../gas/elf/dwarf2-5.s: Error: attempt to get value of unresolved symbol `.L5' ../gas/elf/dwarf2-5.s: Error: attempt to get value of unresolved symbol `.L11' ../gas/elf/dwarf2-5.s: Error: attempt to get value of unresolved symbol `.L12' So why is that? Well, it turns out that .L5 is defined in terms of .L4, and apparently .L4 is undefined. But .L4 clearly is defined, otherwise we would hit an error when trying to use .L4 a little earlier. There are two copies of .L4! So, symbols are cloned when that should not happen. Symbol cloning is a technique used by gas to support saving the value of symbols that change between uses, but that isn't the case with .L4. Only one value is set and used for .L4, but indeed .L4 was being cloned by symbol_clone_if_forward_ref. This despite no forward refs being present. Also, .L4 is a local symbol and a cursory glance at symbol_clone_if_forward_ref "if (symbolP && !LOCAL_SYMBOL_CHECK (symbolP))" would seem to prevent cloning of local symbols. All is not as it seems though, a curse of using macros. LOCAL_SYMBOL_CHECK modifies its argument if a "struct local_symbol" is converted to the larger "struct symbol", as happens when assigning a view symbol value. That fact results in the recursive call to symbol_clone_if_forward_ref returning a different address for "add_symbol". This problem could have been fixed by using symbol_same_p rather than comparing symbol pointers, but I thought it better to use the real symbol throughout. Note that symbol_find_exact also returns the real symbol for a converted local symbol. Finally, this patch does expose lack of support for forward symbol definitions in various targets. For example: alpha-linux +ERROR: ../ld/testsuite/ld-elf/pr11138-2.c: compilation failed This is caused by view symbol uses. On alpha-linux-gcc (GCC) 8.1.1 20180502 they happen to occur in .byte directives so were silently broken in cases like elf/dwarf2-17 anyway. /tmp/ccvtsMfU.s: Assembler messages: /tmp/ccvtsMfU.s: Fatal error: unhandled relocation type BFD_RELOC_8 /tmp/ccvtsMfU.s: Fatal error: unhandled relocation type BFD_RELOC_8 md_apply_fix on those targets needs to handle fixups that resolve down to a constant. PR 23040 * symbols.c (get_real_sym): New function. (symbol_same_p): Use get_real_sym. (symbol_clone_if_forward_ref): Save real original add_symbol and op_symbol for comparison against that returned from lookup or recursive calls. * dwarf2dbg.c (set_or_check_view): Use expr_section for expression symbols, not absolute_section. (dwarf2_directive_loc): Check symbol_equated_p and tidy cloning of view symbols. * read.c (s_leb128): Don't use deferred_expression.
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.