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In optimized code, a formal parameter's location may be a register (DW_OP_reg*). Fjalar marked such a parameter's location invalid, so it omitted the parameter from the .dtrace file (though not from the .decls file). Even with a valid location, the traversal pointed at a local copy of the register's current value, which had no A and V bits or DynComp tags, and which at function exit no longer held the parameter. At function entrance, save the registers in the FunctionExecutionState, with their A and V bits and (for DynComp) their tags. Read a register parameter from that copy at both entrance and exit, as Fjalar reads stack parameters from the virtual stack. The entrance helper now also declares that it reads R8 through R15 on amd64. Add a regression test, register-params-test.sh.
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Docstring coverage is 58.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 48 functions across 22 files. (2 skipped:… | Write docstrings for the functions missing them to satisfy the coverage threshold. |
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Docstring coverage is 58.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 48 functions across 22 files. (2 skipped: 2 unsupported.)
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- Treat a register location as valid only if it is a single DW_OP_reg of a readable register, the value fits in one register, and the location has no DW_OP_piece. Other locations (e.g., DW_OP_lit*) are skipped instead of reaching an assertion failure. - Replace get_reg and dwarf_reg_string by one table, with bounds-checked accessors used by all callers. - Save and tag only the registers that hold a function's formal parameters (FunctionEntry.paramRegMask). - Remove the unused DWARF evaluation loop in returnArrayVariableWithAddr, and skip register-located parameters there. - Assert that the current execution state matches the function being traversed. - Test a struct split across registers and a floating-point parameter, and skip the test if the compiler does not put every parameter in a register.
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Review comments at @valgrind/fjalar/kvasir/kvasir_main.c:
- Around line 808-828: Update the DynComp register-tag copy in the
parameter-register loop to preserve each incoming byte’s tag. In the code around
`kvasir_with_dyncomp`, retain the tag pointer returned by
`VG_(get_tag_ptr_for_guest_offset)` and use the corresponding byte’s tag when
setting each `entryRegs[i]` byte, rather than copying the first tag to all
bytes.
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📒 Files selected for processing (14)
Makefilevalgrind/fjalar/dwarf.cvalgrind/fjalar/fjalar_include.hvalgrind/fjalar/fjalar_main.cvalgrind/fjalar/fjalar_main.hvalgrind/fjalar/fjalar_runtime.cvalgrind/fjalar/fjalar_traversal.cvalgrind/fjalar/generate_fjalar_entries.cvalgrind/fjalar/kvasir/kvasir_main.cvalgrind/fjalar/tests/register-params-test.shvalgrind/fjalar/tests/register-params.cvalgrind/fjalar/tests/register-params.goalvalgrind/fjalar/typedata.cvalgrind/fjalar/typedata.h
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- valgrind/fjalar/fjalar_main.h
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Fjalar now traces formal parameters whose location is a register (codespecs/fjalar#90). The flex tests have functions with parameters declared `register`, such as addsym's sym, copy_string's str, hashfunct's str, and mkentry's state. At -O0, gcc keeps those in registers, so Fjalar now outputs them. That changes the .counts line numbers and merges some comparability sets in the .comp files.
* Omit a formal parameter whose location Fjalar cannot read from the .decls file too, so that it matches the .dtrace file. * A register parameter occupies no stack slot when computing stack parameter offsets. * Handle a DW_OP_bregN frame base. * Save at most FJALAR_MAX_PARAM_REGS registers per invocation, listed in FunctionEntry.paramRegs, rather than one slot per DWARF register. * Treat DW_OP_bit_piece like DW_OP_piece. * register-params-test.sh fails rather than skips in CI. * Use binutils' register names for debugging output.
- Compute the frame base from a DW_OP_regN location-list entry, not just DW_OP_bregN. - Use the architecture's frame-pointer register in the DW_OP_deref frame-base workaround. - Skip register-params-test.sh when a formal parameter has no location. - Store entryRegs in the virtualStack allocation rather than in every FunctionExecutionState. - Initialize DWARF register names, so debugging output names registers. - Omit a formal parameter whose location contains any operation that Fjalar does not record. - Pass entryRegs to visitVariableGroup rather than reading a global. - Save register values, A and V bits, and DynComp tags in one place.
This was referenced Oct 11, 2026
…ster-params # Conflicts: # valgrind/fjalar/fjalar_main.c # valgrind/fjalar/fjalar_main.h # valgrind/fjalar/fjalar_traversal.c
…ister-params # Conflicts: # Makefile # valgrind/fjalar/fjalar_traversal.c # valgrind/fjalar/generate_fjalar_entries.c
- Declare R8-R15 as read by the function-exit helper, too. - For DW_OP_bregN on the frame pointer, use its value at function entry. - Keep a register-located variable's value alive until visitVariable runs. - Share DW_OP_regN/DW_OP_bregN decoding via dwarf_op_reg_num. - Remove a redundant init_dwarf_regnames_by_elf_machine_code call. - Simplify the x86 register table; keep its size private. - Log when the CFA register cannot be read.
Also correct the comment on dwarf_reg_guest_offsets, which has no -1 entries.
…ster-params # Conflicts: # valgrind/fjalar/fjalar_main.h # valgrind/fjalar/fjalar_traversal.c
returnArrayVariableWithAddr evaluated a formal parameter's DWARF location expression into var_loc but never used the result.
…arf-register-access # Conflicts: # valgrind/fjalar/fjalar_runtime.c
…tack slot to any parameter in a register From codespecs#93: * Record in FunctionEntry.entryRegsMask the readable registers that valid formal-parameter locations use, and save only those at function entrance. * A parameter whose location is a register occupies no stack slot, even if Fjalar cannot read the register. * Remove a dead REGISTER_LOCATION check from returnArrayVariableWithAddr, which never sees formal parameters. * Fold omitted-params-test.sh into register-params-test.sh, which now checks every .decls program point, sorted.
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mernst
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…d-location-op As this pull request's description requires: * location_op_is_supported() accepts DW_OP_reg* for a register that Fjalar can read. extractOneFormalParameterVar sets locationUnsupported for any other register location, so no heuristic makes it valid. * visitVariableGroup asserts that the registers of a valid location were saved at entrance, instead of reading address 0. * The DW_OP_stack_value and DW_OP_piece tests move from omitted-params-test.sh, which codespecs#90 deletes, to register-params-test.sh. Their functions are in stack-params.c, a separate compilation unit, because an unoptimized function in register-params.c changes the comparability of scale's parameters. Use codespecs#91's FJALAR_NUM_DWARF_REGS instead of NUM_READABLE_DWARF_REGS, which counted entries of the get_reg table that codespecs#91 deletes.
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This pull request depends on #91 (which depends on #94), and it contains their commits. Please land #94 and #91 first. After that, this pull request's diff shows only its own change.
In optimized code, a formal parameter's location may be a register (
DW_OP_reg*) rather than a stack slot. Fjalar handled this incorrectly in two ways:extractOneFormalParameterVarsetvalidLoconly for frame-pointer-relative locations, so a register parameter hadvalidLoc == 0, and Fjalar omitted it.visitVariableGrouppointed at a local copy of the register's current value (a pointer that outlived the variable). That copy had no A and V bits, so the value printed asnonsensical; it had no DynComp tags; and at function exit the register no longer held the parameter.With this pull request, if some formal parameter's location uses a register,
enter_functionsaves the registers that the valid parameter locations use, with their A and V bits and DynComp tags, in a newentryRegsfield ofFunctionExecutionState, indexed by DWARF register number.visitVariableGroupreads a register parameter from that copy at both entrance and exit, just as it reads stack parameters from the virtual stack. Because the copy is per invocation, recursion is handled.This pull request also makes the
.declsand.dtracefiles declare the same variables. Fjalar omits a formal parameter whose location it cannot read (validLoc == 0) from the.dtracefile. But the test was insideif (stackBaseAddr)invisitVariableGroup, so it did not apply when Fjalar writes the.declsfile, the--dump-var-namesfile, or the disambig file, or when it harvests objects. Now the test does not depend onstackBaseAddr. This is a user-visible change: a formal parameter that has a location list (common at-O2) or noDW_AT_locationis no longer declared, and a--var-list-fileor disambig file that names such a parameter no longer matches it.A location relative to a register (
DW_OP_breg*) also uses the register's entrance value, so a parameter's address at exit is its address at entrance even if the body has overwritten the register or the epilogue has restored it.At
-O0, gcc keeps a parameter in a register only if the parameter is declaredregister. Otherwise, the.declsand.dtraceoutput (with--dyncomp) is unchanged on the programs I tried. The flex Kvasir tests do declareregisterparameters, so their expected output changes; codespecs/daikon#900 updates it, and the pull requests should be merged together.New test
valgrind/fjalar/tests/register-params-test.sh, run bymake fjalar-test, checks values at entrance and exit, DynComp comparability, and that a parameter split across registers and a parameter in a floating-point register appear in neither the.declsnor the.dtracefile. It fails without this change.Not addressed: a parameter whose location is a location list (for example, one kept in a callee-saved register across a call) is still omitted.
The test compiles with
-gno-variable-location-views, so that it does not depend on #89.