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Ensure that alignment is at most 16 and we do not cause UB

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This commit is contained in:
Rangi42
2025-08-06 15:18:35 -04:00
parent f9a55bd5cd
commit 3f6db080b4
1 changed files with 68 additions and 58 deletions
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94
src/asm/section.cpp
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@@ -105,7 +105,6 @@ Section *sect_FindSectionByName(std::string const &name) {
return search != sectionMap.end() ? &sectionList[search->second] : nullptr;
}
#define mask(align) ((1U << (align)) - 1)
#define sectError(...) \
do { \
error(__VA_ARGS__); \
@@ -115,9 +114,16 @@ Section *sect_FindSectionByName(std::string const &name) {
static unsigned int mergeSectUnion(
Section &sect, SectionType type, uint32_t org, uint8_t alignment, uint16_t alignOffset
) {
assume(alignment < 16); // Should be ensured by the caller
unsigned int nbSectErrors = 0;
assume(alignment < 16); // Should be ensured by the caller
uint32_t alignSize = 1u << alignment;
uint32_t alignMask = alignSize - 1;
assume(sect.align <= 16); // Left-shifting by 32 or more would be UB
uint32_t sectAlignSize = 1u << sect.align;
uint32_t sectAlignMask = sectAlignSize - 1;
// Unionized sections only need "compatible" constraints, and they end up with the strictest
// combination of both.
if (sect_HasData(type)) {
@@ -130,10 +136,10 @@ static unsigned int mergeSectUnion(
sectError(
"Section already declared as fixed at different address $%04" PRIx32, sect.org
);
} else if (sect.align != 0 && (mask(sect.align) & (org - sect.alignOfs))) {
} else if (sect.align != 0 && ((org - sect.alignOfs) & sectAlignMask)) {
sectError(
"Section already declared as aligned to %u bytes (offset %" PRIu16 ")",
1U << sect.align,
"Section already declared as aligned to %" PRIu32 " bytes (offset %" PRIu16 ")",
sectAlignSize,
sect.alignOfs
);
} else {
@@ -144,17 +150,18 @@ static unsigned int mergeSectUnion(
} else if (alignment != 0) {
// Make sure any fixed address given is compatible
if (sect.org != UINT32_MAX) {
if ((sect.org - alignOffset) & mask(alignment)) {
if ((sect.org - alignOffset) & alignMask) {
sectError(
"Section already declared as fixed at incompatible address $%04" PRIx32,
sect.org
);
}
// Check if alignment offsets are compatible
} else if ((alignOffset & mask(sect.align)) != (sect.alignOfs & mask(alignment))) {
} else if ((alignOffset & sectAlignMask) != (sect.alignOfs & alignMask)) {
sectError(
"Section already declared with incompatible %u-byte alignment (offset %" PRIu16 ")",
1U << sect.align,
"Section already declared with incompatible %" PRIu32
"-byte alignment (offset %" PRIu16 ")",
sectAlignSize,
sect.alignOfs
);
} else if (alignment > sect.align) {
@@ -169,9 +176,16 @@ static unsigned int mergeSectUnion(
static unsigned int
mergeFragments(Section &sect, uint32_t org, uint8_t alignment, uint16_t alignOffset) {
assume(alignment < 16); // Should be ensured by the caller
unsigned int nbSectErrors = 0;
assume(alignment < 16); // Should be ensured by the caller
uint32_t alignSize = 1u << alignment;
uint32_t alignMask = alignSize - 1;
assume(sect.align <= 16); // Left-shifting by 32 or more would be UB
uint32_t sectAlignSize = 1u << sect.align;
uint32_t sectAlignMask = sectAlignSize - 1;
// Fragments only need "compatible" constraints, and they end up with the strictest
// combination of both.
// The merging is however performed at the *end* of the original section!
@@ -183,10 +197,10 @@ static unsigned int
sectError(
"Section already declared as fixed at incompatible address $%04" PRIx32, sect.org
);
} else if (sect.align != 0 && (mask(sect.align) & (curOrg - sect.alignOfs))) {
} else if (sect.align != 0 && ((curOrg - sect.alignOfs) & sectAlignMask)) {
sectError(
"Section already declared as aligned to %u bytes (offset %" PRIu16 ")",
1U << sect.align,
"Section already declared as aligned to %" PRIu32 " bytes (offset %" PRIu16 ")",
sectAlignSize,
sect.alignOfs
);
} else {
@@ -195,25 +209,26 @@ static unsigned int
}
} else if (alignment != 0) {
int32_t curOfs = (alignOffset - sect.size) % (1U << alignment);
int32_t curOfs = (alignOffset - sect.size) % alignSize;
if (curOfs < 0) {
curOfs += 1U << alignment;
curOfs += alignSize;
}
// Make sure any fixed address given is compatible
if (sect.org != UINT32_MAX) {
if ((sect.org - curOfs) & mask(alignment)) {
if ((sect.org - curOfs) & alignMask) {
sectError(
"Section already declared as fixed at incompatible address $%04" PRIx32,
sect.org
);
}
// Check if alignment offsets are compatible
} else if ((curOfs & mask(sect.align)) != (sect.alignOfs & mask(alignment))) {
} else if ((curOfs & sectAlignMask) != (sect.alignOfs & alignMask)) {
sectError(
"Section already declared with incompatible %u-byte alignment (offset %" PRIu16 ")",
1U << sect.align,
"Section already declared with incompatible %" PRIu32
"-byte alignment (offset %" PRIu16 ")",
sectAlignSize,
sect.alignOfs
);
} else if (alignment > sect.align) {
@@ -356,6 +371,10 @@ static Section *getSection(
uint8_t alignment = attrs.alignment;
uint16_t alignOffset = attrs.alignOfs;
assume(alignment <= 16); // Should be ensured by the caller
uint32_t alignSize = 1u << alignment;
uint32_t alignMask = alignSize - 1;
// First, validate parameters, and normalize them if applicable
if (bank != UINT32_MAX) {
@@ -377,11 +396,11 @@ static Section *getSection(
bank = sectionTypeInfo[type].firstBank;
}
if (alignOffset >= 1 << alignment) {
if (alignOffset >= alignSize) {
error(
"Alignment offset (%" PRIu16 ") must be smaller than alignment size (%u)",
"Alignment offset (%" PRIu16 ") must be smaller than alignment size (%" PRIu32 ")",
alignOffset,
1U << alignment
alignSize
);
alignOffset = 0;
}
@@ -400,19 +419,13 @@ static Section *getSection(
}
if (alignment != 0) {
if (alignment > 16) {
error("Alignment must be between 0 and 16, not %u", alignment);
alignment = 16;
}
// It doesn't make sense to have both alignment and org set
uint32_t mask = mask(alignment);
if (org != UINT32_MAX) {
if ((org - alignOffset) & mask) {
if ((org - alignOffset) & alignMask) {
error("Section \"%s\"'s fixed address doesn't match its alignment", name.c_str());
}
alignment = 0; // Ignore it if it's satisfied
} else if (sectionTypeInfo[type].startAddr & mask) {
} else if (sectionTypeInfo[type].startAddr & alignMask) {
error(
"Section \"%s\"'s alignment cannot be attained in %s",
name.c_str(),
@@ -609,8 +622,12 @@ void sect_AlignPC(uint8_t alignment, uint16_t offset) {
return;
}
assume(alignment <= 16); // Should be ensured by the caller
uint32_t alignSize = 1u << alignment;
Section *sect = sect_GetSymbolSection();
uint32_t alignSize = 1 << alignment; // Size of an aligned "block"
assume(sect->align <= 16); // Left-shifting by 32 or more would be UB
uint32_t sectAlignSize = 1u << sect->align;
if (sect->org != UINT32_MAX) {
if (uint32_t actualOffset = (sect->org + curOffset) % alignSize; actualOffset != offset) {
@@ -624,26 +641,20 @@ void sect_AlignPC(uint8_t alignment, uint16_t offset) {
actualOffset
);
}
} else {
if (uint32_t actualOffset = (sect->alignOfs + curOffset) % alignSize,
sectAlignSize = 1 << sect->align;
} else if (uint32_t actualOffset = (sect->alignOfs + curOffset) % alignSize;
sect->align != 0 && actualOffset % sectAlignSize != offset % sectAlignSize) {
error(
"Section is misaligned ($%04" PRIx32
" bytes into the section, expected ALIGN[%" PRIu32 ", %" PRIu32
"], got ALIGN[%" PRIu32 ", %" PRIu32 "])",
"Section is misaligned ($%04" PRIx32 " bytes into the section, expected ALIGN[%" PRIu32
", %" PRIu32 "], got ALIGN[%" PRIu32 ", %" PRIu32 "])",
curOffset,
alignment,
offset,
alignment,
actualOffset
);
} else if (alignment >= 16) {
} else if (alignment == 16) {
// Treat an alignment large enough as fixing the address.
// Note that this also ensures that a section's alignment never becomes 16 or greater.
if (alignment > 16) {
error("Alignment must be between 0 and 16, not %u", alignment);
}
sect->align = 0; // Reset the alignment, since we're fixing the address.
sect->org = offset - curOffset;
} else if (alignment > sect->align) {
@@ -651,7 +662,6 @@ void sect_AlignPC(uint8_t alignment, uint16_t offset) {
// We need `(sect->alignOfs + curOffset) % alignSize == offset`
sect->alignOfs = (offset - curOffset) % alignSize;
}
}
}
static void growSection(uint32_t growth) {