From 7622049e0bef81fab900860400838bc977449892 Mon Sep 17 00:00:00 2001 From: Senthil Kumar Selvaraj Date: Thu, 16 May 2019 12:12:33 +0530 Subject: [PATCH] Fix PR 24571 - Relaxation does not shorten jmp or call to target at pc-relative range boundary The range check done to transform an absolute call/jump to a pc-relative one is off-by-one, and that causes this shortening optimization to be missed if the branch target is right at the range boundary. In the non-shrinkable case, the range is what is mentioned in the ISA - -4094 bytes in the backward direction, and 4096 bytes in the positive direction. In the shrinkable case, the forward jump range increases by two bytes (deleted because of the shortening from call/jmp to rcall/rjmp), and therefore, the range is -4094 in the reverse, and 4098 in the positive direction. Fix the ranges for !shrinkable and shrinkable cases, and add a test caes to ensure jumps to max forward and backward ranges get relaxed to rjmp. --- bfd/ChangeLog | 6 ++++++ bfd/elf32-avr.c | 18 +++++++++++++++--- ld/ChangeLog | 6 ++++++ .../ld-avr/relax-insn-at-range-boundary.d | 17 +++++++++++++++++ .../ld-avr/relax-insn-at-range-boundary.s | 11 +++++++++++ 5 files changed, 55 insertions(+), 3 deletions(-) create mode 100644 ld/testsuite/ld-avr/relax-insn-at-range-boundary.d create mode 100644 ld/testsuite/ld-avr/relax-insn-at-range-boundary.s diff --git a/bfd/ChangeLog b/bfd/ChangeLog index 0d7eda4f708..7d22cc03d3e 100644 --- a/bfd/ChangeLog +++ b/bfd/ChangeLog @@ -1,3 +1,9 @@ +2019-05-21 Senthil Kumar Selvaraj + + PR ld/24571 + * bfd/elf32-avr.c (elf32_avr_relax_section): Adjust range check + when computing distance_short_enough. + 2019-05-21 Senthil Kumar Selvaraj PR ld/24564 diff --git a/bfd/elf32-avr.c b/bfd/elf32-avr.c index f8a843e16c8..34ad42300dd 100644 --- a/bfd/elf32-avr.c +++ b/bfd/elf32-avr.c @@ -2643,16 +2643,28 @@ elf32_avr_relax_section (bfd *abfd, /* Compute the distance from this insn to the branch target. */ gap = value - dot; + /* The ISA manual states that addressable range is PC - 2k + 1 to + PC + 2k. In bytes, that would be -4094 <= PC <= 4096. The range + is shifted one word to the right, because pc-relative instructions + implicitly add one word i.e. rjmp 0 jumps to next insn, not the + current one. + Therefore, for the !shrinkable case, the range is as above. + If shrinkable, then the current code only deletes bytes 3 and + 4 of the absolute call/jmp, so the forward jump range increases + by 2 bytes, but the backward (negative) jump range remains + the same. */ + + /* Check if the gap falls in the range that can be accommodated in 13bits signed (It is 12bits when encoded, as we deal with word addressing). */ - if (!shrinkable && ((int) gap >= -4096 && (int) gap <= 4095)) + if (!shrinkable && ((int) gap >= -4094 && (int) gap <= 4096)) distance_short_enough = 1; /* If shrinkable, then we can check for a range of distance which - is two bytes farther on both the directions because the call + is two bytes farther on the positive direction because the call or jump target will be closer by two bytes after the relaxation. */ - else if (shrinkable && ((int) gap >= -4094 && (int) gap <= 4097)) + else if (shrinkable && ((int) gap >= -4094 && (int) gap <= 4098)) distance_short_enough = 1; /* Here we handle the wrap-around case. E.g. for a 16k device diff --git a/ld/ChangeLog b/ld/ChangeLog index 20be135c6e0..e038e400333 100644 --- a/ld/ChangeLog +++ b/ld/ChangeLog @@ -1,3 +1,9 @@ +2019-05-21 Senthil Kumar Selvaraj + + PR ld/24571 + * ld/testsuite/ld-avr/relax-insn-at-range-boundary.d: New test. + * ld/testsuite/ld-avr/relax-insn-at-range-boundary.s: New test. + 2019-05-21 Senthil Kumar Selvaraj PR ld/24564 diff --git a/ld/testsuite/ld-avr/relax-insn-at-range-boundary.d b/ld/testsuite/ld-avr/relax-insn-at-range-boundary.d new file mode 100644 index 00000000000..6183896f7c0 --- /dev/null +++ b/ld/testsuite/ld-avr/relax-insn-at-range-boundary.d @@ -0,0 +1,17 @@ +#name: AVR relaxation, jump to symbol at ends of pc-relative range boundary +#as: -mlink-relax -mavr51 +#ld: --relax -mavr51 +#source: relax-insn-at-range-boundary.s +#objdump: -d +#target: avr-*-* + +#... +00000000.* + ... + ffc: 00 00 nop + ffe: 00 c8 rjmp .-4096 ; 0x0 .* + 1000: ff c7 rjmp .+4094 ; 0x2000 + ... + +00002000 : +#... diff --git a/ld/testsuite/ld-avr/relax-insn-at-range-boundary.s b/ld/testsuite/ld-avr/relax-insn-at-range-boundary.s new file mode 100644 index 00000000000..4d710df36d1 --- /dev/null +++ b/ld/testsuite/ld-avr/relax-insn-at-range-boundary.s @@ -0,0 +1,11 @@ +.section ".text", "ax",@progbits +.global main +main: +backward_target: ; Exactly -4094 bytes from jmp + .ds.b 4094, 0 + jmp backward_target + jmp forward_target + .ds.b 4094, 0 +forward_target: ; Exactly 4098 bytes before relax, 4096 bytes after relax + nop + -- 2.30.2