Is qemu-bfin's gdb-stub broken? #5
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If there is a pending DMA operation during ide_bus_reset(), the fact
that the IDEState is already reset before the operation is canceled
can be problematic. In particular, ide_dma_cb() might be called and
then use the reset IDEState which contains the signature after the
reset. When used to construct the IO operation this leads to
ide_get_sector() returning 0 and nsector being 1. This is particularly
bad, because a write command will thus destroy the first sector which
often contains a partition table or similar.
Traces showing the unsolicited write happening with IDEState
0x5595af6949d0 being used after reset:
> ahci_port_write ahci(0x5595af6923f0)[0]: port write [reg:PxSCTL] @ 0x2c: 0x00000300
> ahci_reset_port ahci(0x5595af6923f0)[0]: reset port
> ide_reset IDEstate 0x5595af6949d0
> ide_reset IDEstate 0x5595af694da8
> ide_bus_reset_aio aio_cancel
> dma_aio_cancel dbs=0x7f64600089a0
> dma_blk_cb dbs=0x7f64600089a0 ret=0
> dma_complete dbs=0x7f64600089a0 ret=0 cb=0x5595acd40b30
> ahci_populate_sglist ahci(0x5595af6923f0)[0]
> ahci_dma_prepare_buf ahci(0x5595af6923f0)[0]: prepare buf limit=512 prepared=512
> ide_dma_cb IDEState 0x5595af6949d0; sector_num=0 n=1 cmd=DMA WRITE
> dma_blk_io dbs=0x7f6420802010 bs=0x5595ae2c6c30 offset=0 to_dev=1
> dma_blk_cb dbs=0x7f6420802010 ret=0
> (gdb) p *qiov
> $11 = {iov = 0x7f647c76d840, niov = 1, {{nalloc = 1, local_iov = {iov_base = 0x0,
> iov_len = 512}}, {__pad = "\001\000\000\000\000\000\000\000\000\000\000",
> size = 512}}}
> (gdb) bt
> #0 blk_aio_pwritev (blk=0x5595ae2c6c30, offset=0, qiov=0x7f6420802070, flags=0,
> cb=0x5595ace6f0b0 <dma_blk_cb>, opaque=0x7f6420802010)
> at ../block/block-backend.c:1682
> #1 0x00005595ace6f185 in dma_blk_cb (opaque=0x7f6420802010, ret=<optimized out>)
> at ../softmmu/dma-helpers.c:179
> #2 0x00005595ace6f778 in dma_blk_io (ctx=0x5595ae0609f0,
> sg=sg@entry=0x5595af694d00, offset=offset@entry=0, align=align@entry=512,
> io_func=io_func@entry=0x5595ace6ee30 <dma_blk_write_io_func>,
> io_func_opaque=io_func_opaque@entry=0x5595ae2c6c30,
> cb=0x5595acd40b30 <ide_dma_cb>, opaque=0x5595af6949d0,
> dir=DMA_DIRECTION_TO_DEVICE) at ../softmmu/dma-helpers.c:244
> #3 0x00005595ace6f90a in dma_blk_write (blk=0x5595ae2c6c30,
> sg=sg@entry=0x5595af694d00, offset=offset@entry=0, align=align@entry=512,
> cb=cb@entry=0x5595acd40b30 <ide_dma_cb>, opaque=opaque@entry=0x5595af6949d0)
> at ../softmmu/dma-helpers.c:280
> #4 0x00005595acd40e18 in ide_dma_cb (opaque=0x5595af6949d0, ret=<optimized out>)
> at ../hw/ide/core.c:953
> #5 0x00005595ace6f319 in dma_complete (ret=0, dbs=0x7f64600089a0)
> at ../softmmu/dma-helpers.c:107
> qemu#6 dma_blk_cb (opaque=0x7f64600089a0, ret=0) at ../softmmu/dma-helpers.c:127
> qemu#7 0x00005595ad12227d in blk_aio_complete (acb=0x7f6460005b10)
> at ../block/block-backend.c:1527
> qemu#8 blk_aio_complete (acb=0x7f6460005b10) at ../block/block-backend.c:1524
> qemu#9 blk_aio_write_entry (opaque=0x7f6460005b10) at ../block/block-backend.c:1594
> qemu#10 0x00005595ad258cfb in coroutine_trampoline (i0=<optimized out>,
> i1=<optimized out>) at ../util/coroutine-ucontext.c:177
Signed-off-by: Fiona Ebner <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Tested-by: [email protected]
Message-ID: <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
vapier
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Jan 26, 2024
…ock_status Using fleecing backup like in [0] on a qcow2 image (with metadata preallocation) can lead to the following assertion failure: > bdrv_co_do_block_status: Assertion `!(ret & BDRV_BLOCK_ZERO)' failed. In the reproducer [0], it happens because the BDRV_BLOCK_RECURSE flag will be set by the qcow2 driver, so the caller will recursively check the file child. Then the BDRV_BLOCK_ZERO set too. Later up the call chain, in bdrv_co_do_block_status() for the snapshot-access driver, the assertion failure will happen, because both flags are set. To fix it, clear the recurse flag after the recursive check was done. In detail: > #0 qcow2_co_block_status Returns 0x45 = BDRV_BLOCK_RECURSE | BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID. > #1 bdrv_co_do_block_status Because of the data flag, bdrv_co_do_block_status() will now also set BDRV_BLOCK_ALLOCATED. Because of the recurse flag, bdrv_co_do_block_status() for the bdrv_file child will be called, which returns 0x16 = BDRV_BLOCK_ALLOCATED | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_ZERO. Now the return value inherits the zero flag. Returns 0x57 = BDRV_BLOCK_RECURSE | BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_ALLOCATED | BDRV_BLOCK_ZERO. > #2 bdrv_co_common_block_status_above > #3 bdrv_co_block_status_above > #4 bdrv_co_block_status > #5 cbw_co_snapshot_block_status > qemu#6 bdrv_co_snapshot_block_status > qemu#7 snapshot_access_co_block_status > qemu#8 bdrv_co_do_block_status Return value is propagated all the way up to here, where the assertion failure happens, because BDRV_BLOCK_RECURSE and BDRV_BLOCK_ZERO are both set. > qemu#9 bdrv_co_common_block_status_above > qemu#10 bdrv_co_block_status_above > qemu#11 block_copy_block_status > qemu#12 block_copy_dirty_clusters > qemu#13 block_copy_common > qemu#14 block_copy_async_co_entry > qemu#15 coroutine_trampoline [0]: > #!/bin/bash > rm /tmp/disk.qcow2 > ./qemu-img create /tmp/disk.qcow2 -o preallocation=metadata -f qcow2 1G > ./qemu-img create /tmp/fleecing.qcow2 -f qcow2 1G > ./qemu-img create /tmp/backup.qcow2 -f qcow2 1G > ./qemu-system-x86_64 --qmp stdio \ > --blockdev qcow2,node-name=node0,file.driver=file,file.filename=/tmp/disk.qcow2 \ > --blockdev qcow2,node-name=node1,file.driver=file,file.filename=/tmp/fleecing.qcow2 \ > --blockdev qcow2,node-name=node2,file.driver=file,file.filename=/tmp/backup.qcow2 \ > <<EOF > {"execute": "qmp_capabilities"} > {"execute": "blockdev-add", "arguments": { "driver": "copy-before-write", "file": "node0", "target": "node1", "node-name": "node3" } } > {"execute": "blockdev-add", "arguments": { "driver": "snapshot-access", "file": "node3", "node-name": "snap0" } } > {"execute": "blockdev-backup", "arguments": { "device": "snap0", "target": "node1", "sync": "full", "job-id": "backup0" } } > EOF Signed-off-by: Fiona Ebner <[email protected]> Reviewed-by: Vladimir Sementsov-Ogievskiy <[email protected]> Message-id: [email protected] Signed-off-by: Stefan Hajnoczi <[email protected]>
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Hello.
When trying to debug with gdb while emulating bfin's ELF, I get packet errors.
Is this the intended behavior? Or any plans to support qemu-user's GDB stubs?
Thanks.
Host: Ubuntu 22.04
bfin-linux-gcc: https://toolchains.bootlin.com/
gdb: 13.2 (built from source)
Here are the steps to reproduce:
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