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+id = 1128
+title = "PPC: `spr_write_xer` doesn't set flag bits in `cpu_xer`"
+state = "closed"
+created_at = "2022-07-29T20:50:24.121Z"
+closed_at = "2022-07-29T21:37:44.303Z"
+labels = ["Closed::Invalid"]
+url = "https://gitlab.com/qemu-project/qemu/-/issues/1128"
+host-os = "n/a"
+host-arch = "n/a"
+qemu-version = "commit: cc42559ab129a15554cc485ea9265e34dde7ab5b"
+guest-os = "n/a"
+guest-arch = "n/a"
+description = """`spr_write_xer()` does not set the `ca`, `ov`, `so`, `ca32`, `ov32` etc. flag bits in the `cpu_xer` variable.
+
+In fact it copies all bits from the source `GPR` and _excludes_ each flag bit.
+
+This is not a problem for execution since `spr_read_xer()` gets the flag bits from `cpu_ca/ov/so...` and not from `cpu_xer`.
+
+Nonetheless it is problem for tools which trace the execution in QEMU (e.g. https://github.com/BinaryAnalysisPlatform/qemu). 
+
+A fix would be to remove the `~` in https://gitlab.com/qemu-project/qemu/-/blob/master/target/ppc/translate.c#L481"""
+reproduce = """Haven't found out yet how to debug QEMU so the TCGv values can be investigated. But in general one need to:
+
+- Execute a binary which executes something like:
+```
+r4 = 0xffffffffffffffff
+mtxer r4
+```
+and check the `cpu_xer` value after the `xer` write.
+
+Checking the debug logs (`in_asm,cpu`) doesn't work, since the `xer` value in the logs is not taken directly from `cpu_xer`."""
+additional = """Code ref: https://gitlab.com/qemu-project/qemu/-/blob/master/target/ppc/translate.c#L480-L483"""