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HW Debug API: Better handling of BAS on ARM

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The watchpoint value register contains a 4-byte aligned virtual address,
but the way we set the BAS, which determines the bytes of the word
pointed to by the address that trigger an exception, assumes the
address can be anything. This means that watchpoints did not reliably
work for small types such as characters and shorts, which are not
always 4-byte aligned.  In this patch, if a watchpoint with size < 4
is set, we align the address used to the previous 4-byte boundary and
set the appropriate BAS to trigger an exception for the sub-range
intended by the user.

Signed-off-by: Alwin Joshy <joshyalwin@gmail.com>
This commit is contained in:
Alwin Joshy
2024-08-29 11:45:35 +10:00
committed by Ivan-Velickovic
parent 3862d14fe4
commit dbba75154e
1 changed files with 32 additions and 2 deletions
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34
src/arch/arm/machine/debug.c
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@@ -229,6 +229,19 @@ uint16_t getBpNumFromType(uint16_t bp_num, word_t type)
}
}
static void calculate_wcr_BAS(seL4_Word address, seL4_Word size, seL4_Word *set_address, seL4_Word* bas) {
if (address % 4 == 0) {
*set_address = address;
} else {
*set_address = address & ~0x3; // Align to 4-byte boundary
}
*bas = 0;
for (int i = address - *set_address; i < (address - *set_address) + size; i++) {
*bas |= (1 << i);
}
}
/** Sets up the requested hardware breakpoint register.
*
* Acts as the backend for seL4_TCB_SetBreakpoint. Doesn't actually operate
@@ -290,13 +303,17 @@ void setBreakpoint(tcb_t *t,
} else {
dbg_wcr_t wcr;
writeWvrContext(t, bp_num, vaddr);
word_t bas;
word_t set_vaddr;
calculate_wcr_BAS(vaddr, size, &set_vaddr, &bas);
writeWvrContext(t, bp_num, set_vaddr);
/* Preserve reserved bits */
wcr.words[0] = readWcrContext(t, bp_num);
wcr = dbg_wcr_set_enabled(wcr, 1);
wcr = dbg_wcr_set_pac(wcr, DBGWCR_PRIV_USER);
wcr = dbg_wcr_set_bas(wcr, convertSizeToArch(size));
wcr = dbg_wcr_set_bas(wcr, bas);
wcr = dbg_wcr_set_lsc(wcr, convertAccessToArch(rw));
wcr = dbg_wcr_set_watchpointType(wcr, 0);
wcr = dbg_wcr_set_lbn(wcr, 0);
@@ -449,6 +466,19 @@ int getAndResetActiveBreakpoint(word_t vaddr, word_t reason)
word_t wvr = readWvrCp(i);
wcr.words[0] = readWcrCp(i);
/* Align to the previous word*/
if (!dbg_wcr_get_enabled(wcr) || (vaddr & ~0x3) != wvr) {
continue;
}
if (vaddr % 4 != 0) {
int offset = vaddr % 4;
if ((dbg_wcr_get_bas(wcr) & offset) == 0) {
continue;
}
}
align_mask = convertArchToSize(dbg_wcr_get_bas(wcr));
align_mask = ~(align_mask - 1);