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Clear non-significant bits of address on memory access

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ARMv8 supports tagged address, that is, the top one byte in address
is ignored.  It is always enabled on aarch64-linux.  See
https://www.kernel.org/doc/Documentation/arm64/tagged-pointers.txt

The tag in the tagged address is modeled as non-significant bits in
address, so this patch adds a new gdbarch method significant_addr_bit and
clear the non-significant bits (the top byte in ARMv8) of the virtual
address at the point before passing address to target cache layer.  IOW,
the address used in the target cache layer is already cleared.

Before this patch,
(gdb) x/x 0x0000000000411030
0x411030 <global>:	0x00000000
(gdb) x/x 0xf000000000411030
0xf000000000411030:	Cannot access memory at address 0xf000000000411030

After this patch,

(gdb) x/x 0x0000000000411030
0x411030 <global>:	0x00000000
(gdb) x/x 0xf000000000411030
0xf000000000411030:	0x00000000

Note that I used address_significant in paddress, but it causes a
regression gdb.base/long_long.exp, because gdb clears the non-significant
bits in address, but test still expects them.

p/a val.oct^M
$24 = 0x2ee53977053977^M
(gdb) FAIL: gdb.base/long_long.exp: p/a val.oct

so I defer the change there.

gdb:

2017-12-08  Yao Qi  <yao.qi@linaro.org>

	* aarch64-tdep.c (aarch64_gdbarch_init): Install gdbarch
	significant_addr_bit.
	* gdbarch.sh (significant_addr_bit): New.
	* gdbarch.c, gdbarch.h: Re-generated.
	* target.c (memory_xfer_partial): Call address_significant.
	* utils.c (address_significant): New function.
	* utils.h (address_significant): Declare.

2017-12-08  Yao Qi  <yao.qi@linaro.org>

gdb/testsuite:

	* gdb.arch/aarch64-tagged-pointer.c: New file.
	* gdb.arch/aarch64-tagged-pointer.exp: New file.
This commit is contained in:
Yao Qi
2017-12-08 17:27:03 +00:00
parent 8e481c3ba8
commit a738ea1d41
11 changed files with 193 additions and 0 deletions
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8
gdb/gdbarch.h
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@@ -677,6 +677,14 @@ typedef CORE_ADDR (gdbarch_addr_bits_remove_ftype) (struct gdbarch *gdbarch, COR
extern CORE_ADDR gdbarch_addr_bits_remove (struct gdbarch *gdbarch, CORE_ADDR addr);
extern void set_gdbarch_addr_bits_remove (struct gdbarch *gdbarch, gdbarch_addr_bits_remove_ftype *addr_bits_remove);
/* On some machines, not all bits of an address word are significant.
For example, on AArch64, the top bits of an address known as the "tag"
are ignored by the kernel, the hardware, etc. and can be regarded as
additional data associated with the address. */
extern int gdbarch_significant_addr_bit (struct gdbarch *gdbarch);
extern void set_gdbarch_significant_addr_bit (struct gdbarch *gdbarch, int significant_addr_bit);
/* FIXME/cagney/2001-01-18: This should be split in two. A target method that
indicates if the target needs software single step. An ISA method to
implement it.