From b312488f1046a1b837561a4adf4323e29377cf12 Mon Sep 17 00:00:00 2001 From: Faraz Shahbazker Date: Wed, 5 May 2021 04:51:16 +0530 Subject: sim: mips: Only truncate sign extension bits for 32-bit target models 64-bit BFD for MIPS applies a standard sign extension on all addresses assuming 64-bit target. These bits are required for 64-bit and can only be safely truncated for 32-bit target models. This partially reverts commit b36d953bced0a4fecdde1823abac70ed7038ee95 The sign-extension logic modeled by BFD is an integral part of the MIPS64 architecture spec. It appears in the virtual address map, where sign extension allows for 32-bit compatibility segments [1] with 64-bit addressing. Truncating these addresses prematurely (commit models (-DWITH_TARGET_WORD_BITSIZE=64). In the ISA itself, direct addressing (Load-Upper-Immediate) and indirect addressing (Load-Word) both automatically sign-extend their results. These instructions regenerate the sign-extended addresses even if we don't start with one (see pr gdb/19447). Moreover, some instructions like ADD*/SUB* have unpredictable behaviour when an operand is not correctly sign extended [3]. This affects PC-relative addressing in particular, so arithmetic on the link-address generated in the return address register by a jump-and-link is no longer possible, neither is the use of the PC-relative addressing instructions provided by MIPSR6. [1] "MIPS64 Architecture for Programmers Volume III: The MIPS64 Privileged Resource Architecture", Document Number: MD00091, Revision 6.02, December 10, 2015, Section 4.3 "Virtual Address Spaces", pp. 29-31 https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00091-2B-MIPS64PRA-AFP-06.03.pdf [2] "MIPS64 Architecture for Programmers Volume II-A: The MIPS64 Instruction Set Reference Manual", Document Number: MD00087, Revision 6.06, December 15, 2016, Section 3.2 "Alphabetical List of Instructions", pp. 321 https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00087-2B-MIPS64BIS-AFP-6.06.pdf [3] "MIPS64 Architecture for Programmers Volume II-A: The MIPS64 Instruction Set Reference Manual", Document Number: MD00087, Revision 6.06, December 15, 2016, Section 3.2 "Alphabetical List of Instructions", pp. 56 https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00087-2B-MIPS64BIS-AFP-6.06.pdf 2021-04-23 Faraz Shahbazker sim/mips/ChangeLog: * interp.c (sim_create_inferior): Only truncate sign extension bits for 32-bit target models . --- sim/mips/ChangeLog | 6 ++++++ sim/mips/interp.c | 11 +++++------ 2 files changed, 11 insertions(+), 6 deletions(-) (limited to 'sim/mips') diff --git a/sim/mips/ChangeLog b/sim/mips/ChangeLog index 85ce1ac..123d722 100644 --- a/sim/mips/ChangeLog +++ b/sim/mips/ChangeLog @@ -1,3 +1,9 @@ +2021-05-22 Faraz Shahbazker + +sim/mips/ChangeLog: + * interp.c (sim_create_inferior): Only truncate sign extension + bits for 32-bit target models. + 2021-05-17 Mike Frysinger * sim-main.h (SIM_HAVE_COMMON_SIM_STATE): Delete. diff --git a/sim/mips/interp.c b/sim/mips/interp.c index 2839715..6e00fd0 100644 --- a/sim/mips/interp.c +++ b/sim/mips/interp.c @@ -1014,12 +1014,11 @@ sim_create_inferior (SIM_DESC sd, struct bfd *abfd, sim_cpu *cpu = STATE_CPU (sd, cpu_nr); sim_cia pc = bfd_get_start_address (abfd); - /* We need to undo brain-dead bfd behavior where it sign-extends - addresses that are supposed to be unsigned. See the mips bfd - sign_extend_vma setting. We have to check the ELF data itself - in order to handle o32 & n32 ABIs. */ - if (abfd->tdata.elf_obj_data->elf_header->e_ident[EI_CLASS] == - ELFCLASS32) + /* The 64-bit BFD sign-extends MIPS addresses to model + 32-bit compatibility segments with 64-bit addressing. + These addresses work as is on 64-bit targets but + can be truncated for 32-bit targets. */ + if (WITH_TARGET_WORD_BITSIZE == 32) pc = (unsigned32) pc; CPU_PC_SET (cpu, pc); -- cgit v1.1