fix: improve linker script expression section semantics by vishruth-thimmaiah · Pull Request #2731 · wild-linker/wild

vishruth-thimmaiah · 2026-10-15T01:22:39Z

This PR make a bunch of improvements to how different types of expressions(absolute, section relative, numbers) interact with each other. Fixes:

Symbols preserve their section indexes across redefinition.
Preserving section relativity across ternary, MIN, and MAX expressions
Logical, bitwise, and comparison operators producing absolute symbols

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

davidlattimore

Here are some extra related tests that currently fail:

diff --git a/wild/tests/sources/elf/linker-script-expression-sections/absolute-arithmetic.ld b/wild/tests/sources/elf/linker-script-expression-sections/absolute-arithmetic.ld
new file mode 100644
index 0000000000..d221ad17da
--- /dev/null
+++ b/wild/tests/sources/elf/linker-script-expression-sections/absolute-arithmetic.ld
@@ -0,0 +1,13 @@
+ENTRY(_start)
+SECTIONS {
+    .text 0x10000 : {
+        section_start = .;
+        *(.text*)
+    }
+}
+
+/* These operations produce absolute values even with a section operand. */
+product = section_start * 2;
+quotient = section_start / 2;
+shifted = section_start >> 1;
+reverse_difference = 0x20000 - section_start;
diff --git a/wild/tests/sources/elf/linker-script-expression-sections/addr-alias.ld b/wild/tests/sources/elf/linker-script-expression-sections/addr-alias.ld
new file mode 100644
index 0000000000..7463c19edc
--- /dev/null
+++ b/wild/tests/sources/elf/linker-script-expression-sections/addr-alias.ld
@@ -0,0 +1,9 @@
+ENTRY(_start)
+SECTIONS {
+    .text 0x10000 : {
+        *(.text*)
+        /* ADDR retains the referenced section, including through arithmetic. */
+        section_addr = ADDR(.text);
+        after_addr = section_addr + 0x10;
+    }
+}
diff --git a/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c b/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c
new file mode 100644
index 0000000000..114b4c89d5
--- /dev/null
+++ b/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c
@@ -0,0 +1,37 @@ void _start(void) {}
+//#AbstractConfig:base
+//#RunEnabled:false
+//#DiffEnabled:false
+//#ReferenceLinkers:bfd
+
+//#Config:addr-alias:base
+//#ReferenceLinkers:bfd,lld
+//#LinkArgs:-T ./addr-alias.ld
+//#ExpectSym:after_addr section=".text",address=0x10010
+//#ExpectSym:section_addr section=".text",address=0x10000
+
+//#Config:min-max-number:base
+//#LinkArgs:-T ./min-max-number.ld
+//#ExpectSym:min_right section=".text",address=0x10000
+//#ExpectSym:min_left section=".text",address=0x10000
+//#ExpectSym:max_right section=".text",address=0x10010
+//#ExpectSym:max_left section=".text",address=0x10010
+
+//#Config:min-max-location:base
+//#LinkArgs:-T ./min-max-location.ld
+//#ExpectSym:padded_end section=".text",address=0x10100
+
+//#Config:absolute-arithmetic:base
+//#ReferenceLinkers:bfd,lld
+//#LinkArgs:-T ./absolute-arithmetic.ld
+//#ExpectSym:product is_abs=true,address=0x20000
+//#ExpectSym:quotient is_abs=true,address=0x8000
+//#ExpectSym:shifted is_abs=true,address=0x8000
+//#ExpectSym:reverse_difference is_abs=true,address=0x10000
+
+//#Config:relative-plus-absolute:base
+//#LinkArgs:-T ./relative-plus-absolute.ld
+//#ExpectSym:absolute_offset is_abs=true,address=0x10
+//#ExpectSym:derived is_abs=true,address=0x10010
+//#ExpectSym:derived_reverse is_abs=true,address=0x10010
+
+void _start(void) {}
diff --git a/wild/tests/sources/elf/linker-script-expression-sections/min-max-location.ld b/wild/tests/sources/elf/linker-script-expression-sections/min-max-location.ld
new file mode 100644
index 0000000000..fb8e396591
--- /dev/null
+++ b/wild/tests/sources/elf/linker-script-expression-sections/min-max-location.ld
@@ -0,0 +1,9 @@
+ENTRY(_start)
+SECTIONS {
+    .text 0x10000 : {
+        *(.text*)
+        /* The same conversion must work during early layout evaluation. */
+        . = MAX(., 0x100);
+        padded_end = .;
+    }
+}
diff --git a/wild/tests/sources/elf/linker-script-expression-sections/min-max-number.ld b/wild/tests/sources/elf/linker-script-expression-sections/min-max-number.ld
new file mode 100644
index 0000000000..edfcd004b3
--- /dev/null
+++ b/wild/tests/sources/elf/linker-script-expression-sections/min-max-number.ld
@@ -0,0 +1,12 @@
+ENTRY(_start)
+SECTIONS {
+    .text 0x10000 : {
+        section_start = .;
+        *(.text*)
+        /* GNU ld compares section offsets with numeric operands here. */
+        min_right = MIN(section_start, 0x10);
+        min_left = MIN(0x10, section_start);
+        max_right = MAX(section_start, 0x10);
+        max_left = MAX(0x10, section_start);
+    }
+}
diff --git a/wild/tests/sources/elf/linker-script-expression-sections/relative-plus-absolute.ld b/wild/tests/sources/elf/linker-script-expression-sections/relative-plus-absolute.ld
new file mode 100644
index 0000000000..7a3aa3490b
--- /dev/null
+++ b/wild/tests/sources/elf/linker-script-expression-sections/relative-plus-absolute.ld
@@ -0,0 +1,14 @@
+ENTRY(_start)
+absolute_offset = 0x10;
+
+SECTIONS {
+    .text 0x10000 : {
+        section_start = .;
+        *(.text*)
+    }
+}
+
+/* A named absolute symbol exercises Relative/Absolute, rather than
+   Relative/Number. GNU ld makes both sums absolute outside a section. */
+derived = section_start + absolute_offset;
+derived_reverse = absolute_offset + section_start;

davidlattimore · 2026-10-15T02:53:07Z

-        let resolution = resolutions[canonical_symbol_id.as_usize()]
-            .as_mut()
-            .ok_or_else(|| redirect.missing_resolution(def_info.name))?;
+        if is_absolute && redirect.loc.relative_section_id().is_some() {


This function both reads and writes redirect.loc, making it a little hard to follow what's going on. Is there an alternative that would be more readable?

I've added a Redirect::update_for_evaluated_value method here.

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

davidlattimore · 2026-10-20T21:29:42Z

            }
        }

+        if exp.assertions.is_abs {


Some of the tests have is_abs=false, but it looks like this will skip any check if that's the case

Fixed, I've replaced any is_abs=false checks with an explicit section check.

davidlattimore · 2026-10-20T21:34:30Z

+    _section_layouts: &OutputSectionMap<OutputRecordLayout>,
+    op: impl FnOnce(u64, u64) -> Result<u64>,
+) -> Result<EvaluatedValue> {
+    let value_kind = if is_in_section {


Does it matter what type we produce for expressions like LOADADDR(.text) & 0xffff? Do we agree with the other linkers in that case with regard to whether the result is absolute to section-relative?

lld and ld deviate on how they handle absolute results, and I was previously matching whichever linkers' behavior was more convenient. I've updated it to match bfd more closely.

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

davidlattimore · 2026-10-21T09:37:06Z

+            (ExpressionValueKind::Number, ExpressionValueKind::Number) => {
+                ExpressionValueKind::Number
+            }
+            (ExpressionValueKind::Relative(sec), _) | (_, ExpressionValueKind::Relative(sec)) => {


It looks like subtracting a relative offset from another relative offset should produce an absolute:

diff --git a/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c b/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c index 086c2547af..41623d5217 100644 --- a/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c +++ b/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c @@ -17,6 +17,11 @@ //#ExpectSym:max_right section=".text",address=0x10010 //#ExpectSym:max_left section=".text",address=0x10010 +//#Config:nested-subtraction:base +//#ReferenceLinkers:bfd,lld +//#LinkArgs:-T ./nested-subtraction.ld +//#ExpectSym:difference is_abs=true,address=0x20 + //#Config:min-max-location:base //#LinkArgs:-T ./min-max-location.ld //#ExpectSym:padded_end section=".text",address=0x10100 diff --git a/wild/tests/sources/elf/linker-script-expression-sections/nested-subtraction.ld b/wild/tests/sources/elf/linker-script-expression-sections/nested-subtraction.ld new file mode 100644 index 0000000000..702b662e0d --- /dev/null +++ b/wild/tests/sources/elf/linker-script-expression-sections/nested-subtraction.ld @@ -0,0 +1,9 @@ +ENTRY(_start) +SECTIONS { + .text 0x10000 : { + section_start = .; + section_end = section_start + 0x20; + difference = MIN(section_end - section_start, LOADADDR(.text)); + *(.text*) + } +}

Fixed, along with a few other previously failing tests.

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

davidlattimore

Looks like cross-section expressions aren't doing the right thing:

diff --git a/wild/tests/sources/elf/linker-script-expression-sections/cross-section-offsets.ld b/wild/tests/sources/elf/linker-script-expression-sections/cross-section-offsets.ld
new file mode 100644
index 0000000000..fa2f4bcf68
--- /dev/null
+++ b/wild/tests/sources/elf/linker-script-expression-sections/cross-section-offsets.ld
@@ -0,0 +1,12 @@
+ENTRY(_start)
+SECTIONS {
+    .data 0x20000 : {
+        data_start = .;
+        KEEP(*(.data*))
+    }
+    .text 0x10000 : {
+        cross_min = MIN(data_start, 0x10);
+        cross_mul = data_start * 2;
+        *(.text*)
+    }
+}
diff --git a/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c b/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c
index 28e5cb80b3..f989ee66c0 100644
--- a/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c
+++ b/wild/tests/sources/elf/linker-script-expression-sections/linker-script-expression-sections.c
@@ -17,6 +17,11 @@
 //#ExpectSym:max_right section=".text",address=0x10010
 //#ExpectSym:max_left section=".text",address=0x10010
 
+//#Config:cross-section-offsets:base
+//#LinkArgs:-T ./cross-section-offsets.ld
+//#ExpectSym:cross_min section=".data",address=0x20000
+//#ExpectSym:cross_mul section=".data",address=0x20000
+
 //#Config:nested-subtraction:base
 //#ReferenceLinkers:bfd,lld
 //#LinkArgs:-T ./nested-subtraction.ld

feat: improve linker script expression section semantics

289cc51

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

vishruth-thimmaiah marked this pull request as ready for review October 15, 2026 01:29

vishruth-thimmaiah requested a review from davidlattimore October 15, 2026 01:29

davidlattimore reviewed Oct 15, 2026

View reviewed changes

address comments

b094bd8

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

vishruth-thimmaiah requested a review from davidlattimore October 20, 2026 19:35

davidlattimore reviewed Oct 20, 2026

View reviewed changes

fix: match bfd behavior for more expressions

7a8abc8

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

vishruth-thimmaiah requested a review from davidlattimore October 21, 2026 09:32

davidlattimore reviewed Oct 21, 2026

View reviewed changes

vishruth-thimmaiah added 3 commits October 21, 2026 20:39

fix failing test

165ae40

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

fixes for more failing tests

a7f86d2

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

force alignment of 0x1

d41153a

Signed-off-by: Vishruth Thimmaiah <vishruththimmaiah@gmail.com>

vishruth-thimmaiah requested a review from davidlattimore October 22, 2026 06:20

davidlattimore reviewed Oct 22, 2026

View reviewed changes

Navigation Menu

Repository navigation

fix: improve linker script expression section semantics - #2731

fix: improve linker script expression section semantics#2731
vishruth-thimmaiah wants to merge 6 commits into
wild-linker:mainfrom
vishruth-thimmaiah:dyn_expressions

vishruth-thimmaiah commented Oct 15, 2026

Uh oh!

davidlattimore left a comment

Uh oh!

Uh oh!

davidlattimore Oct 15, 2026

Uh oh!

vishruth-thimmaiah Oct 20, 2026

Uh oh!

Uh oh!

davidlattimore Oct 20, 2026

Uh oh!

vishruth-thimmaiah Oct 21, 2026

Uh oh!

davidlattimore Oct 20, 2026

Uh oh!

vishruth-thimmaiah Oct 21, 2026

Uh oh!

davidlattimore Oct 21, 2026

Uh oh!

vishruth-thimmaiah Oct 22, 2026

Uh oh!

davidlattimore left a comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Conversation

vishruth-thimmaiah commented Oct 15, 2026

Uh oh!

davidlattimore left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

davidlattimore left a comment

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants