Wilco Dijkstra <wilco.dijks...@arm.com> writes:
> ping
>
> In aarch64_classify_symbol symbols are allowed full-range offsets on
> relocations.
> This means the offset can use all of the +/-4GB offset, leaving no offset
> available
> for the symbol itself. This results in relocation overflow and link-time
> errors
> for simple expressions like &global_char + 0xffffff00.
If global_char really is a char then isn't that UB? I guess we still
have to compile it without error though...
> To avoid this, limit the offset to +/-1MB so that the symbol needs to be
> within a
> 3.9GB offset from its references. For the tiny code model use a 64KB
> offset, allowing
> most of the 1MB range for code/data between the symbol and its references.
These new values seem a bit magical. Would it work for the original
testcase to use FORCE_TO_MEM if !offset_within_block_p (x, offset)?
Richard
> Bootstrapped on AArch64, passes regress, OK for commit?
>
> ChangeLog:
> 2018-11-09 Wilco Dijkstra <wdijk...@arm.com>
>
> gcc/
> * config/aarch64/aarch64.c (aarch64_classify_symbol):
> Apply reasonable limit to symbol offsets.
>
> testsuite/
> * gcc.target/aarch64/symbol-range.c (foo): Set new limit.
> * gcc.target/aarch64/symbol-range-tiny.c (foo): Likewise.
>
> --
>
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index
> 83453d03095018eddd1801e71ef3836849267444..0023cb37bbae5afe9387840c1bb6b43586d4fac2
> 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -13047,26 +13047,26 @@ aarch64_classify_symbol (rtx x, HOST_WIDE_INT
> offset)
> the offset does not cause overflow of the final address.
> But
> we have no way of knowing the address of symbol at compile
> time
> so we can't accurately say if the distance between the PC
> and
> - symbol + offset is outside the addressible range of +/-1M in
> the
> - TINY code model. So we rely on images not being greater than
> - 1M and cap the offset at 1M and anything beyond 1M will have
> to
> - be loaded using an alternative mechanism. Furthermore if the
> - symbol is a weak reference to something that isn't known to
> - resolve to a symbol in this module, then force to memory. */
> + symbol + offset is outside the addressible range of +/-1MB
> in the
> + TINY code model. So we limit the maximum offset to +/-64KB
> and
> + assume the offset to the symbol is not larger than +/-(1MB -
> 64KB).
> + Furthermore force to memory if the symbol is a weak
> reference to
> + something that doesn't resolve to a symbol in this module.
> */
> if ((SYMBOL_REF_WEAK (x)
> && !aarch64_symbol_binds_local_p (x))
> - || !IN_RANGE (offset, -1048575, 1048575))
> + || !IN_RANGE (offset, -0x10000, 0x10000))
> return SYMBOL_FORCE_TO_MEM;
> +
> return SYMBOL_TINY_ABSOLUTE;
>
> case AARCH64_CMODEL_SMALL:
> /* Same reasoning as the tiny code model, but the offset cap
> here is
> - 4G. */
> + 1MB, allowing +/-3.9GB for the offset to the symbol. */
> if ((SYMBOL_REF_WEAK (x)
> && !aarch64_symbol_binds_local_p (x))
> - || !IN_RANGE (offset, HOST_WIDE_INT_C (-4294967263),
> - HOST_WIDE_INT_C (4294967264)))
> + || !IN_RANGE (offset, -0x100000, 0x100000))
> return SYMBOL_FORCE_TO_MEM;
> +
> return SYMBOL_SMALL_ABSOLUTE;
>
> case AARCH64_CMODEL_TINY_PIC:
> diff --git a/gcc/testsuite/gcc.target/aarch64/symbol-range-tiny.c
> b/gcc/testsuite/gcc.target/aarch64/symbol-range-tiny.c
> index
> d7e46b059e41f2672b3a1da5506fa8944e752e01..d49ff4dbe5786ef6d343d2b90052c09676dd7fe5
> 100644
> --- a/gcc/testsuite/gcc.target/aarch64/symbol-range-tiny.c
> +++ b/gcc/testsuite/gcc.target/aarch64/symbol-range-tiny.c
> @@ -1,12 +1,12 @@
> -/* { dg-do compile } */
> +/* { dg-do link } */
> /* { dg-options "-O3 -save-temps -mcmodel=tiny" } */
>
> -int fixed_regs[0x00200000];
> +char fixed_regs[0x00200000];
>
> int
> -foo()
> +main ()
> {
> - return fixed_regs[0x00080000];
> + return fixed_regs[0x000ff000];
> }
>
> /* { dg-final { scan-assembler-not "adr\tx\[0-9\]+, fixed_regs\\\+" } }
> */
> diff --git a/gcc/testsuite/gcc.target/aarch64/symbol-range.c
> b/gcc/testsuite/gcc.target/aarch64/symbol-range.c
> index
> 6574cf4310430b847e77ea56bf8f20ef312d53e4..75c87c12f08004c153efc5192e5cfab566c089db
> 100644
> --- a/gcc/testsuite/gcc.target/aarch64/symbol-range.c
> +++ b/gcc/testsuite/gcc.target/aarch64/symbol-range.c
> @@ -1,12 +1,12 @@
> -/* { dg-do compile } */
> +/* { dg-do link } */
> /* { dg-options "-O3 -save-temps -mcmodel=small" } */
>
> -int fixed_regs[0x200000000ULL];
> +char fixed_regs[0x200000000ULL];
>
> int
> -foo()
> +main ()
> {
> - return fixed_regs[0x100000000ULL];
> + return fixed_regs[0xfffff000ULL];
> }
>
> /* { dg-final { scan-assembler-not "adrp\tx\[0-9\]+, fixed_regs\\\+" } }
> */
