Attempt to fix ARM32 Windows #685

bdbai · 2024-12-20T13:55:05Z

Currently thumbv7a-pc-windows-msvc and thumbv7a-pc-windows-msvc fails to build due to lack of a few symbols generated by windows-targets. As backtrace being a dependency of Rust std, build-std feature targeting these platforms also fails. The fix here is definitely not a good idea which is modifying a generated file, but it shows the possibility to have the issue solved at least to unblock build-std on these platforms.

This was how I verified it using 1.85.0-nightly (9e136a30a 2024-12-19) toolchain:

cargo +nightly build -Z build-std=core,alloc,panic_abort --target thumbv7a-uwp-windows-msvc --no-default-features
cargo +nightly build -Z build-std=core,alloc,panic_abort --target thumbv7a-pc-windows-msvc --no-default-features

which produced the following output:

cargo +nightly build -Z build-std=core,alloc,panic_abort --target thumbv7a-uwp-windows-msvc --no-default-features                                         ─╯
   Compiling backtrace v0.3.74 (<path-to>\backtrace-rs)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.21s

cargo +nightly build -Z build-std=core,alloc,panic_abort --target thumbv7a-pc-windows-msvc --no-default-features                                          ─╯
   Compiling backtrace v0.3.74 (<path-to>\backtrace-rs)
warning: unnecessary `unsafe` block
   --> src\backtrace\dbghelp32.rs:218:5
    |
218 |     unsafe {
    |     ^^^^^^ unnecessary `unsafe` block
    |
    = note: `#[warn(unused_unsafe)]` on by default

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:115:21
    |
115 |                       DBGHELP.$name().unwrap()
    |                       ^^^^^^^ mutable reference to mutable static
...
128 | / dbghelp! {
129 | |     extern "system" {
130 | |         fn SymGetOptions() -> u32;
131 | |         fn SymSetOptions(options: u32) -> u32;
...   |
223 | | }
    | |_- in this macro invocation
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives
    = note: `#[warn(static_mut_refs)]` on by default
    = note: this warning originates in the macro `dbghelp` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:115:21
    |
115 |                       DBGHELP.$name().unwrap()
    |                       ^^^^^^^ mutable reference to mutable static
...
128 | / dbghelp! {
129 | |     extern "system" {
130 | |         fn SymGetOptions() -> u32;
131 | |         fn SymSetOptions(options: u32) -> u32;
...   |
223 | | }
    | |_- in this macro invocation
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives
    = note: this warning originates in the macro `dbghelp` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:321:9
    |
321 |         DBGHELP.ensure_open()?;
    |         ^^^^^^^^^^^^^^^^^^^^^ mutable reference to mutable static
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:333:20
    |
333 |         let orig = DBGHELP.SymGetOptions()?();
    |                    ^^^^^^^^^^^^^^^^^^^^^^^ mutable reference to mutable static
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:338:9
    |
338 |         DBGHELP.SymSetOptions()?(orig | SYMOPT_DEFERRED_LOADS);
    |         ^^^^^^^^^^^^^^^^^^^^^^^ mutable reference to mutable static
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:352:9
    |
352 |         DBGHELP.SymInitializeW()?(GetCurrentProcess(), ptr::null_mut(), TRUE);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^ mutable reference to mutable static
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:366:12
    |
366 |         if DBGHELP.SymGetSearchPathW()?(
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ mutable reference to mutable static
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:386:9
    |
386 |         DBGHELP.EnumerateLoadedModulesW64()?(
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ mutable reference to mutable static
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives

warning: creating a mutable reference to mutable static is discouraged
   --> src\dbghelp.rs:395:9
    |
395 |         DBGHELP.SymSetSearchPathW()?(GetCurrentProcess(), new_search_path.as_ptr());
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ mutable reference to mutable static
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html>
    = note: mutable references to mutable statics are dangerous; it's undefined behavior if any other pointer to the static is used or if any other reference is created for the static while the mutable reference lives

warning: `backtrace` (lib) generated 24 warnings (14 duplicates)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.23s

Any input on better ways to handle this will be appreciated! In Rust std I can see it's solved here https://github.com/rust-lang/rust/blob/8a1f8039a7ded79d3d4fe97b110016d89f2b11e2/src/tools/generate-windows-sys/src/main.rs#L8 . Not sure if we can apply something similar here.

Xref: #572 #634

workingjubilee · 2024-12-25T05:55:39Z

@bdbai I am curious what use the 32-bit Windows Arm target is being put to? It is a target unmaintained by the OS vendor... as in, the entire OS is unmaintained for that target... and no one has signed up to maintain the target on the Rust end.

As for the CONTEXT structure, the std definition provided that you linked to is an uninhabited type (no variants), so it cannot actually be interacted with in the conventional sense... hmm...

bdbai · 2024-12-25T06:52:13Z

@workingjubilee

I am curious what use the 32-bit Windows Arm target is being put to?

Some examples running Windows ARM32: Surface RT, Windows Phone and Windows 10 IoT Core

As for the CONTEXT structure, the std definition provided that you linked to is an uninhabited type (no variants), so it cannot actually be interacted with in the conventional sense... hmm...

In std the CONTEXT structure for ARM is only used in pointer form (like https://github.com/rust-lang/rust/blob/41f2f5c0b7d5fb68685030edc62e66a21cae38ef/library/std/src/sys/pal/windows/c/windows_sys.rs#L65) so we didn't bother to fill up all fields inside but instead treat it as an opaque FFI type. However in backtrace we are actually reading the values inside so the complete definition is required.

workingjubilee · 2024-12-25T06:58:54Z

@bdbai Yes, we don't really have support for any of those targets except for their 64-bit versions. But I wasn't really asking you to quote OS names at me, I'm curious what you actually use it for.

bdbai · 2024-12-25T07:05:32Z

@workingjubilee Personally I am writing UWP apps (https://github.com/YtFlow/YtFlowApp) specifically targeting both desktop and mobile as some users including me are still using Windows Phone. The core part is written in Rust hence needs to cross compile to thumbv7a-uwp-windows-msvc.

workingjubilee · 2024-12-25T07:06:57Z

I see! @ChrisDenton You lost the bet, I suppose?

@bdbai Do you have a citation for the 32-bit Arm Windows target CONTEXT definition? It is, for perhaps obvious reasons, hard to find on Microsoft's documentation.

bdbai · 2024-12-25T07:10:18Z

fyi the definitions are migrated from winapi crate here https://github.com/retep998/winapi-rs/blob/5b1829956ef645f3c2f8236ba18bb198ca4c2468/src/um/winnt.rs#L1468

bdbai · 2024-12-25T07:19:46Z

Copying these from Windows SDK (10.0.22621.0):

//
// Specify the number of breakpoints and watchpoints that the OS
// will track. Architecturally, ARM supports up to 16. In practice,
// however, almost no one implements more than 4 of each.
//

#define ARM_MAX_BREAKPOINTS     8
#define ARM_MAX_WATCHPOINTS     1

//
// Context Frame
//
//  This frame has a several purposes: 1) it is used as an argument to
//  NtContinue, 2) it is used to constuct a call frame for APC delivery,
//  and 3) it is used in the user level thread creation routines.
//
//
// The flags field within this record controls the contents of a CONTEXT
// record.
//
// If the context record is used as an input parameter, then for each
// portion of the context record controlled by a flag whose value is
// set, it is assumed that that portion of the context record contains
// valid context. If the context record is being used to modify a threads
// context, then only that portion of the threads context is modified.
//
// If the context record is used as an output parameter to capture the
// context of a thread, then only those portions of the thread's context
// corresponding to set flags will be returned.
//
// CONTEXT_CONTROL specifies Sp, Lr, Pc, and Cpsr
//
// CONTEXT_INTEGER specifies R0-R12
//
// CONTEXT_FLOATING_POINT specifies Q0-Q15 / D0-D31 / S0-S31
//
// CONTEXT_DEBUG_REGISTERS specifies up to 16 of DBGBVR, DBGBCR, DBGWVR,
//      DBGWCR.
//

typedef struct _NEON128 {
    ULONGLONG Low;
    LONGLONG High;
} NEON128, *PNEON128;

typedef struct DECLSPEC_ALIGN(8) DECLSPEC_NOINITALL _CONTEXT {

    //
    // Control flags.
    //

    DWORD ContextFlags;

    //
    // Integer registers
    //

    DWORD R0;
    DWORD R1;
    DWORD R2;
    DWORD R3;
    DWORD R4;
    DWORD R5;
    DWORD R6;
    DWORD R7;
    DWORD R8;
    DWORD R9;
    DWORD R10;
    DWORD R11;
    DWORD R12;

    //
    // Control Registers
    //

    DWORD Sp;
    DWORD Lr;
    DWORD Pc;
    DWORD Cpsr;

    //
    // Floating Point/NEON Registers
    //

    DWORD Fpscr;
    DWORD Padding;
    union {
        NEON128 Q[16];
        ULONGLONG D[32];
        DWORD S[32];
    } DUMMYUNIONNAME;

    //
    // Debug registers
    //

    DWORD Bvr[ARM_MAX_BREAKPOINTS];
    DWORD Bcr[ARM_MAX_BREAKPOINTS];
    DWORD Wvr[ARM_MAX_WATCHPOINTS];
    DWORD Wcr[ARM_MAX_WATCHPOINTS];

    DWORD Padding2[2];

} CONTEXT, *PCONTEXT;

workingjubilee · 2024-12-25T07:54:27Z

src/windows_sys.rs

+
+        #[repr(C)]
+        #[derive(Clone, Copy)]
+        pub struct CONTEXT_u([u64; 32]);


This should be an actual union that matches the anon union declaration as exactly as possible. The name is unimportant, so let us call it CONTEXT_FloatRegs.

Fixed in d468f71

workingjubilee · 2024-12-25T07:57:59Z

src/windows_sys.rs

+            pub R10: u32,
+            pub R11: u32,
+            pub R12: u32,
+            pub Sp: u32,


Suggested change

pub Sp: u32,

// Control registers

pub Sp: u32,

Fixed in d468f71

workingjubilee · 2024-12-25T07:58:11Z

src/windows_sys.rs

+            pub Lr: u32,
+            pub Pc: u32,
+            pub Cpsr: u32,
+            pub Fpsrc: u32,


Suggested change

pub Fpsrc: u32,

// Floating-point registers

pub Fpsrc: u32,

Fixed in d468f71

workingjubilee · 2024-12-25T07:58:30Z

src/windows_sys.rs

+            pub Fpsrc: u32,
+            pub Padding: u32,
+            pub u: CONTEXT_u,
+            pub Bvr: [u32; ARM_MAX_BREAKPOINTS],


Suggested change

pub Bvr: [u32; ARM_MAX_BREAKPOINTS],

// Debug registers

pub Bvr: [u32; ARM_MAX_BREAKPOINTS],

Fixed in d468f71

workingjubilee · 2024-12-25T09:59:32Z

Thank you. I suppose we will have to think a little on where exactly to put the shim filling, hm.

workingjubilee requested changes Dec 25, 2024

View reviewed changes

bdbai requested a review from workingjubilee December 25, 2024 08:26

bdbai mentioned this pull request Jan 1, 2025

Add UWP (msvc) target support page rust-lang/rust#134996

Open

workingjubilee closed this Jan 2, 2025

workingjubilee reopened this Jan 2, 2025

bdbai added 2 commits January 2, 2025 15:06

Attempt to fix arm32 Windows

2e117c6

Match arm definitions with winsdk

c88b77e

workingjubilee force-pushed the fix/win-arm32 branch from d468f71 to c88b77e Compare January 2, 2025 23:09

workingjubilee closed this Jan 3, 2025

workingjubilee reopened this Jan 3, 2025

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Attempt to fix ARM32 Windows #685

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workingjubilee commented Dec 25, 2024

	pub Bvr: [u32; ARM_MAX_BREAKPOINTS],
	// Debug registers
	pub Bvr: [u32; ARM_MAX_BREAKPOINTS],

Attempt to fix ARM32 Windows #685

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Attempt to fix ARM32 Windows #685

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